#include "cache.h"
#include "attr.h"
#include "run-command.h"
#include "quote.h"
#include "sigchain.h"

/*
 * convert.c - convert a file when checking it out and checking it in.
 *
 * This should use the pathname to decide on whether it wants to do some
 * more interesting conversions (automatic gzip/unzip, general format
 * conversions etc etc), but by default it just does automatic CRLF<->LF
 * translation when the "text" attribute or "auto_crlf" option is set.
 */

enum crlf_action {
        CRLF_GUESS = -1,
        CRLF_BINARY = 0,
        CRLF_TEXT,
        CRLF_INPUT,
        CRLF_CRLF,
        CRLF_AUTO
};

struct text_stat {
        /* NUL, CR, LF and CRLF counts */
        unsigned nul, cr, lf, crlf;

        /* These are just approximations! */
        unsigned printable, nonprintable;
};

static void gather_stats(const char *buf, unsigned long size, struct text_stat *stats)
{
        unsigned long i;

        memset(stats, 0, sizeof(*stats));

        for (i = 0; i < size; i++) {
                unsigned char c = buf[i];
                if (c == '\r') {
                        stats->cr++;
                        if (i+1 < size && buf[i+1] == '\n')
                                stats->crlf++;
                        continue;
                }
                if (c == '\n') {
                        stats->lf++;
                        continue;
                }
                if (c == 127)
                        /* DEL */
                        stats->nonprintable++;
                else if (c < 32) {
                        switch (c) {
                                /* BS, HT, ESC and FF */
                        case '\b': case '\t': case '\033': case '\014':
                                stats->printable++;
                                break;
                        case 0:
                                stats->nul++;
                                /* fall through */
                        default:
                                stats->nonprintable++;
                        }
                }
                else
                        stats->printable++;
        }

        /* If file ends with EOF then don't count this EOF as non-printable. */
        if (size >= 1 && buf[size-1] == '\032')
                stats->nonprintable--;
}

/*
 * The same heuristics as diff.c::mmfile_is_binary()
 */
static int is_binary(unsigned long size, struct text_stat *stats)
{

        if (stats->nul)
                return 1;
        if ((stats->printable >> 7) < stats->nonprintable)
                return 1;
        /*
         * Other heuristics? Average line length might be relevant,
         * as might LF vs CR vs CRLF counts..
         *
         * NOTE! It might be normal to have a low ratio of CRLF to LF
         * (somebody starts with a LF-only file and edits it with an editor
         * that adds CRLF only to lines that are added..). But do  we
         * want to support CR-only? Probably not.
         */
        return 0;
}

static enum eol output_eol(enum crlf_action crlf_action)
{
        switch (crlf_action) {
        case CRLF_BINARY:
                return EOL_UNSET;
        case CRLF_CRLF:
                return EOL_CRLF;
        case CRLF_INPUT:
                return EOL_LF;
        case CRLF_GUESS:
                if (!auto_crlf)
                        return EOL_UNSET;
                /* fall through */
        case CRLF_TEXT:
        case CRLF_AUTO:
                if (auto_crlf == AUTO_CRLF_TRUE)
                        return EOL_CRLF;
                else if (auto_crlf == AUTO_CRLF_INPUT)
                        return EOL_LF;
                else if (core_eol == EOL_UNSET)
                        return EOL_NATIVE;
        }
        return core_eol;
}

static void check_safe_crlf(const char *path, enum crlf_action crlf_action,
                            struct text_stat *stats, enum safe_crlf checksafe)
{
        if (!checksafe)
                return;

        if (output_eol(crlf_action) == EOL_LF) {
                /*
                 * CRLFs would not be restored by checkout:
                 * check if we'd remove CRLFs
                 */
                if (stats->crlf) {
                        if (checksafe == SAFE_CRLF_WARN)
                                warning("CRLF will be replaced by LF in %s.\nThe file will have its original line endings in your working directory.", path);
                        else /* i.e. SAFE_CRLF_FAIL */
                                die("CRLF would be replaced by LF in %s.", path);
                }
        } else if (output_eol(crlf_action) == EOL_CRLF) {
                /*
                 * CRLFs would be added by checkout:
                 * check if we have "naked" LFs
                 */
                if (stats->lf != stats->crlf) {
                        if (checksafe == SAFE_CRLF_WARN)
                                warning("LF will be replaced by CRLF in %s.\nThe file will have its original line endings in your working directory.", path);
                        else /* i.e. SAFE_CRLF_FAIL */
                                die("LF would be replaced by CRLF in %s", path);
                }
        }
}

static int has_cr_in_index(const char *path)
{
        unsigned long sz;
        void *data;
        int has_cr;

        data = read_blob_data_from_cache(path, &sz);
        if (!data)
                return 0;
        has_cr = memchr(data, '\r', sz) != NULL;
        free(data);
        return has_cr;
}

static int crlf_to_git(const char *path, const char *src, size_t len,
                       struct strbuf *buf,
                       enum crlf_action crlf_action, enum safe_crlf checksafe)
{
        struct text_stat stats;
        char *dst;

        if (crlf_action == CRLF_BINARY ||
            (crlf_action == CRLF_GUESS && auto_crlf == AUTO_CRLF_FALSE) ||
            (src && !len))
                return 0;

        /*
         * If we are doing a dry-run and have no source buffer, there is
         * nothing to analyze; we must assume we would convert.
         */
        if (!buf && !src)
                return 1;

        gather_stats(src, len, &stats);

        if (crlf_action == CRLF_AUTO || crlf_action == CRLF_GUESS) {
                /*
                 * We're currently not going to even try to convert stuff
                 * that has bare CR characters. Does anybody do that crazy
                 * stuff?
                 */
                if (stats.cr != stats.crlf)
                        return 0;

                /*
                 * And add some heuristics for binary vs text, of course...
                 */
                if (is_binary(len, &stats))
                        return 0;

                if (crlf_action == CRLF_GUESS) {
                        /*
                         * If the file in the index has any CR in it, do not convert.
                         * This is the new safer autocrlf handling.
                         */
                        if (has_cr_in_index(path))
                                return 0;
                }
        }

        check_safe_crlf(path, crlf_action, &stats, checksafe);

        /* Optimization: No CR? Nothing to convert, regardless. */
        if (!stats.cr)
                return 0;

        /*
         * At this point all of our source analysis is done, and we are sure we
         * would convert. If we are in dry-run mode, we can give an answer.
         */
        if (!buf)
                return 1;

        /* only grow if not in place */
        if (strbuf_avail(buf) + buf->len < len)
                strbuf_grow(buf, len - buf->len);
        dst = buf->buf;
        if (crlf_action == CRLF_AUTO || crlf_action == CRLF_GUESS) {
                /*
                 * If we guessed, we already know we rejected a file with
                 * lone CR, and we can strip a CR without looking at what
                 * follow it.
                 */
                do {
                        unsigned char c = *src++;
                        if (c != '\r')
                                *dst++ = c;
                } while (--len);
        } else {
                do {
                        unsigned char c = *src++;
                        if (! (c == '\r' && (1 < len && *src == '\n')))
                                *dst++ = c;
                } while (--len);
        }
        strbuf_setlen(buf, dst - buf->buf);
        return 1;
}

static int crlf_to_worktree(const char *path, const char *src, size_t len,
                            struct strbuf *buf, enum crlf_action crlf_action)
{
        char *to_free = NULL;
        struct text_stat stats;

        if (!len || output_eol(crlf_action) != EOL_CRLF)
                return 0;

        gather_stats(src, len, &stats);

        /* No LF? Nothing to convert, regardless. */
        if (!stats.lf)
                return 0;

        /* Was it already in CRLF format? */
        if (stats.lf == stats.crlf)
                return 0;

        if (crlf_action == CRLF_AUTO || crlf_action == CRLF_GUESS) {
                if (crlf_action == CRLF_GUESS) {
                        /* If we have any CR or CRLF line endings, we do not touch it */
                        /* This is the new safer autocrlf-handling */
                        if (stats.cr > 0 || stats.crlf > 0)
                                return 0;
                }

                /* If we have any bare CR characters, we're not going to touch it */
                if (stats.cr != stats.crlf)
                        return 0;

                if (is_binary(len, &stats))
                        return 0;
        }

        /* are we "faking" in place editing ? */
        if (src == buf->buf)
                to_free = strbuf_detach(buf, NULL);

        strbuf_grow(buf, len + stats.lf - stats.crlf);
        for (;;) {
                const char *nl = memchr(src, '\n', len);
                if (!nl)
                        break;
                if (nl > src && nl[-1] == '\r') {
                        strbuf_add(buf, src, nl + 1 - src);
                } else {
                        strbuf_add(buf, src, nl - src);
                        strbuf_addstr(buf, "\r\n");
                }
                len -= nl + 1 - src;
                src  = nl + 1;
        }
        strbuf_add(buf, src, len);

        free(to_free);
        return 1;
}

struct filter_params {
        const char *src;
        unsigned long size;
        const char *cmd;
        const char *path;
};

static int filter_buffer(int in, int out, void *data)
{
        /*
         * Spawn cmd and feed the buffer contents through its stdin.
         */
        struct child_process child_process;
        struct filter_params *params = (struct filter_params *)data;
        int write_err, status;
        const char *argv[] = { NULL, NULL };

        /* apply % substitution to cmd */
        struct strbuf cmd = STRBUF_INIT;
        struct strbuf path = STRBUF_INIT;
        struct strbuf_expand_dict_entry dict[] = {
                { "f", NULL, },
                { NULL, NULL, },
        };

        /* quote the path to preserve spaces, etc. */
        sq_quote_buf(&path, params->path);
        dict[0].value = path.buf;

        /* expand all %f with the quoted path */
        strbuf_expand(&cmd, params->cmd, strbuf_expand_dict_cb, &dict);
        strbuf_release(&path);

        argv[0] = cmd.buf;

        memset(&child_process, 0, sizeof(child_process));
        child_process.argv = argv;
        child_process.use_shell = 1;
        child_process.in = -1;
        child_process.out = out;

        if (start_command(&child_process))
                return error("cannot fork to run external filter %s", params->cmd);

        sigchain_push(SIGPIPE, SIG_IGN);

        write_err = (write_in_full(child_process.in, params->src, params->size) < 0);
        if (close(child_process.in))
                write_err = 1;
        if (write_err)
                error("cannot feed the input to external filter %s", params->cmd);

        sigchain_pop(SIGPIPE);

        status = finish_command(&child_process);
        if (status)
                error("external filter %s failed %d", params->cmd, status);

        strbuf_release(&cmd);
        return (write_err || status);
}

static int apply_filter(const char *path, const char *src, size_t len,
                        struct strbuf *dst, const char *cmd)
{
        /*
         * Create a pipeline to have the command filter the buffer's
         * contents.
         *
         * (child --> cmd) --> us
         */
        int ret = 1;
        struct strbuf nbuf = STRBUF_INIT;
        struct async async;
        struct filter_params params;

        if (!cmd)
                return 0;

        if (!dst)
                return 1;

        memset(&async, 0, sizeof(async));
        async.proc = filter_buffer;
        async.data = &params;
        async.out = -1;
        params.src = src;
        params.size = len;
        params.cmd = cmd;
        params.path = path;

        fflush(NULL);
        if (start_async(&async))
                return 0;       /* error was already reported */

        if (strbuf_read(&nbuf, async.out, len) < 0) {
                error("read from external filter %s failed", cmd);
                ret = 0;
        }
        if (close(async.out)) {
                error("read from external filter %s failed", cmd);
                ret = 0;
        }
        if (finish_async(&async)) {
                error("external filter %s failed", cmd);
                ret = 0;
        }

        if (ret) {
                strbuf_swap(dst, &nbuf);
        }
        strbuf_release(&nbuf);
        return ret;
}

static struct convert_driver {
        const char *name;
        struct convert_driver *next;
        const char *smudge;
        const char *clean;
        int required;
} *user_convert, **user_convert_tail;

static int read_convert_config(const char *var, const char *value, void *cb)
{
        const char *key, *name;
        int namelen;
        struct convert_driver *drv;

        /*
         * External conversion drivers are configured using
         * "filter.<name>.variable".
         */
        if (parse_config_key(var, "filter", &name, &namelen, &key) < 0 || !name)
                return 0;
        for (drv = user_convert; drv; drv = drv->next)
                if (!strncmp(drv->name, name, namelen) && !drv->name[namelen])
                        break;
        if (!drv) {
                drv = xcalloc(1, sizeof(struct convert_driver));
                drv->name = xmemdupz(name, namelen);
                *user_convert_tail = drv;
                user_convert_tail = &(drv->next);
        }

        /*
         * filter.<name>.smudge and filter.<name>.clean specifies
         * the command line:
         *
         *      command-line
         *
         * The command-line will not be interpolated in any way.
         */

        if (!strcmp("smudge", key))
                return git_config_string(&drv->smudge, var, value);

        if (!strcmp("clean", key))
                return git_config_string(&drv->clean, var, value);

        if (!strcmp("required", key)) {
                drv->required = git_config_bool(var, value);
                return 0;
        }

        return 0;
}

static int count_ident(const char *cp, unsigned long size)
{
        /*
         * "$Id: 0000000000000000000000000000000000000000 $" <=> "$Id$"
         */
        int cnt = 0;
        char ch;

        while (size) {
                ch = *cp++;
                size--;
                if (ch != '$')
                        continue;
                if (size < 3)
                        break;
                if (memcmp("Id", cp, 2))
                        continue;
                ch = cp[2];
                cp += 3;
                size -= 3;
                if (ch == '$')
                        cnt++; /* $Id$ */
                if (ch != ':')
                        continue;

                /*
                 * "$Id: ... "; scan up to the closing dollar sign and discard.
                 */
                while (size) {
                        ch = *cp++;
                        size--;
                        if (ch == '$') {
                                cnt++;
                                break;
                        }
                        if (ch == '\n')
                                break;
                }
        }
        return cnt;
}

static int ident_to_git(const char *path, const char *src, size_t len,
                        struct strbuf *buf, int ident)
{
        char *dst, *dollar;

        if (!ident || (src && !count_ident(src, len)))
                return 0;

        if (!buf)
                return 1;

        /* only grow if not in place */
        if (strbuf_avail(buf) + buf->len < len)
                strbuf_grow(buf, len - buf->len);
        dst = buf->buf;
        for (;;) {
                dollar = memchr(src, '$', len);
                if (!dollar)
                        break;
                memmove(dst, src, dollar + 1 - src);
                dst += dollar + 1 - src;
                len -= dollar + 1 - src;
                src  = dollar + 1;

                if (len > 3 && !memcmp(src, "Id:", 3)) {
                        dollar = memchr(src + 3, '$', len - 3);
                        if (!dollar)
                                break;
                        if (memchr(src + 3, '\n', dollar - src - 3)) {
                                /* Line break before the next dollar. */
                                continue;
                        }

                        memcpy(dst, "Id$", 3);
                        dst += 3;
                        len -= dollar + 1 - src;
                        src  = dollar + 1;
                }
        }
        memmove(dst, src, len);
        strbuf_setlen(buf, dst + len - buf->buf);
        return 1;
}

static int ident_to_worktree(const char *path, const char *src, size_t len,
                             struct strbuf *buf, int ident)
{
        unsigned char sha1[20];
        char *to_free = NULL, *dollar, *spc;
        int cnt;

        if (!ident)
                return 0;

        cnt = count_ident(src, len);
        if (!cnt)
                return 0;

        /* are we "faking" in place editing ? */
        if (src == buf->buf)
                to_free = strbuf_detach(buf, NULL);
        hash_sha1_file(src, len, "blob", sha1);

        strbuf_grow(buf, len + cnt * 43);
        for (;;) {
                /* step 1: run to the next '$' */
                dollar = memchr(src, '$', len);
                if (!dollar)
                        break;
                strbuf_add(buf, src, dollar + 1 - src);
                len -= dollar + 1 - src;
                src  = dollar + 1;

                /* step 2: does it looks like a bit like Id:xxx$ or Id$ ? */
                if (len < 3 || memcmp("Id", src, 2))
                        continue;

                /* step 3: skip over Id$ or Id:xxxxx$ */
                if (src[2] == '$') {
                        src += 3;
                        len -= 3;
                } else if (src[2] == ':') {
                        /*
                         * It's possible that an expanded Id has crept its way into the
                         * repository, we cope with that by stripping the expansion out.
                         * This is probably not a good idea, since it will cause changes
                         * on checkout, which won't go away by stash, but let's keep it
                         * for git-style ids.
                         */
                        dollar = memchr(src + 3, '$', len - 3);
                        if (!dollar) {
                                /* incomplete keyword, no more '$', so just quit the loop */
                                break;
                        }

                        if (memchr(src + 3, '\n', dollar - src - 3)) {
                                /* Line break before the next dollar. */
                                continue;
                        }

                        spc = memchr(src + 4, ' ', dollar - src - 4);
                        if (spc && spc < dollar-1) {
                                /* There are spaces in unexpected places.
                                 * This is probably an id from some other
                                 * versioning system. Keep it for now.
                                 */
                                continue;
                        }

                        len -= dollar + 1 - src;
                        src  = dollar + 1;
                } else {
                        /* it wasn't a "Id$" or "Id:xxxx$" */
                        continue;
                }

                /* step 4: substitute */
                strbuf_addstr(buf, "Id: ");
                strbuf_add(buf, sha1_to_hex(sha1), 40);
                strbuf_addstr(buf, " $");
        }
        strbuf_add(buf, src, len);

        free(to_free);
        return 1;
}

static enum crlf_action git_path_check_crlf(const char *path, struct git_attr_check *check)
{
        const char *value = check->value;

        if (ATTR_TRUE(value))
                return CRLF_TEXT;
        else if (ATTR_FALSE(value))
                return CRLF_BINARY;
        else if (ATTR_UNSET(value))
                ;
        else if (!strcmp(value, "input"))
                return CRLF_INPUT;
        else if (!strcmp(value, "auto"))
                return CRLF_AUTO;
        return CRLF_GUESS;
}

static enum eol git_path_check_eol(const char *path, struct git_attr_check *check)
{
        const char *value = check->value;

        if (ATTR_UNSET(value))
                ;
        else if (!strcmp(value, "lf"))
                return EOL_LF;
        else if (!strcmp(value, "crlf"))
                return EOL_CRLF;
        return EOL_UNSET;
}

static struct convert_driver *git_path_check_convert(const char *path,
                                             struct git_attr_check *check)
{
        const char *value = check->value;
        struct convert_driver *drv;

        if (ATTR_TRUE(value) || ATTR_FALSE(value) || ATTR_UNSET(value))
                return NULL;
        for (drv = user_convert; drv; drv = drv->next)
                if (!strcmp(value, drv->name))
                        return drv;
        return NULL;
}

static int git_path_check_ident(const char *path, struct git_attr_check *check)
{
        const char *value = check->value;

        return !!ATTR_TRUE(value);
}

static enum crlf_action input_crlf_action(enum crlf_action text_attr, enum eol eol_attr)
{
        if (text_attr == CRLF_BINARY)
                return CRLF_BINARY;
        if (eol_attr == EOL_LF)
                return CRLF_INPUT;
        if (eol_attr == EOL_CRLF)
                return CRLF_CRLF;
        return text_attr;
}

struct conv_attrs {
        struct convert_driver *drv;
        enum crlf_action crlf_action;
        enum eol eol_attr;
        int ident;
};

static const char *conv_attr_name[] = {
        "crlf", "ident", "filter", "eol", "text",
};
#define NUM_CONV_ATTRS ARRAY_SIZE(conv_attr_name)

static void convert_attrs(struct conv_attrs *ca, const char *path)
{
        int i;
        static struct git_attr_check ccheck[NUM_CONV_ATTRS];

        if (!ccheck[0].attr) {
                for (i = 0; i < NUM_CONV_ATTRS; i++)
                        ccheck[i].attr = git_attr(conv_attr_name[i]);
                user_convert_tail = &user_convert;
                git_config(read_convert_config, NULL);
        }

        if (!git_check_attr(path, NUM_CONV_ATTRS, ccheck)) {
                ca->crlf_action = git_path_check_crlf(path, ccheck + 4);
                if (ca->crlf_action == CRLF_GUESS)
                        ca->crlf_action = git_path_check_crlf(path, ccheck + 0);
                ca->ident = git_path_check_ident(path, ccheck + 1);
                ca->drv = git_path_check_convert(path, ccheck + 2);
                ca->eol_attr = git_path_check_eol(path, ccheck + 3);
        } else {
                ca->drv = NULL;
                ca->crlf_action = CRLF_GUESS;
                ca->eol_attr = EOL_UNSET;
                ca->ident = 0;
        }
}

int convert_to_git(const char *path, const char *src, size_t len,
                   struct strbuf *dst, enum safe_crlf checksafe)
{
        int ret = 0;
        const char *filter = NULL;
        int required = 0;
        struct conv_attrs ca;

        convert_attrs(&ca, path);
        if (ca.drv) {
                filter = ca.drv->clean;
                required = ca.drv->required;
        }

        ret |= apply_filter(path, src, len, dst, filter);
        if (!ret && required)
                die("%s: clean filter '%s' failed", path, ca.drv->name);

        if (ret && dst) {
                src = dst->buf;
                len = dst->len;
        }
        ca.crlf_action = input_crlf_action(ca.crlf_action, ca.eol_attr);
        ret |= crlf_to_git(path, src, len, dst, ca.crlf_action, checksafe);
        if (ret && dst) {
                src = dst->buf;
                len = dst->len;
        }
        return ret | ident_to_git(path, src, len, dst, ca.ident);
}

static int convert_to_working_tree_internal(const char *path, const char *src,
                                            size_t len, struct strbuf *dst,
                                            int normalizing)
{
        int ret = 0, ret_filter = 0;
        const char *filter = NULL;
        int required = 0;
        struct conv_attrs ca;

        convert_attrs(&ca, path);
        if (ca.drv) {
                filter = ca.drv->smudge;
                required = ca.drv->required;
        }

        ret |= ident_to_worktree(path, src, len, dst, ca.ident);
        if (ret) {
                src = dst->buf;
                len = dst->len;
        }
        /*
         * CRLF conversion can be skipped if normalizing, unless there
         * is a smudge filter.  The filter might expect CRLFs.
         */
        if (filter || !normalizing) {
                ca.crlf_action = input_crlf_action(ca.crlf_action, ca.eol_attr);
                ret |= crlf_to_worktree(path, src, len, dst, ca.crlf_action);
                if (ret) {
                        src = dst->buf;
                        len = dst->len;
                }
        }

        ret_filter = apply_filter(path, src, len, dst, filter);
        if (!ret_filter && required)
                die("%s: smudge filter %s failed", path, ca.drv->name);

        return ret | ret_filter;
}

int convert_to_working_tree(const char *path, const char *src, size_t len, struct strbuf *dst)
{
        return convert_to_working_tree_internal(path, src, len, dst, 0);
}

int renormalize_buffer(const char *path, const char *src, size_t len, struct strbuf *dst)
{
        int ret = convert_to_working_tree_internal(path, src, len, dst, 1);
        if (ret) {
                src = dst->buf;
                len = dst->len;
        }
        return ret | convert_to_git(path, src, len, dst, SAFE_CRLF_FALSE);
}

/*****************************************************************
 *
 * Streaming converison support
 *
 *****************************************************************/

typedef int (*filter_fn)(struct stream_filter *,
                         const char *input, size_t *isize_p,
                         char *output, size_t *osize_p);
typedef void (*free_fn)(struct stream_filter *);

struct stream_filter_vtbl {
        filter_fn filter;
        free_fn free;
};

struct stream_filter {
        struct stream_filter_vtbl *vtbl;
};

static int null_filter_fn(struct stream_filter *filter,
                          const char *input, size_t *isize_p,
                          char *output, size_t *osize_p)
{
        size_t count;

        if (!input)
                return 0; /* we do not keep any states */
        count = *isize_p;
        if (*osize_p < count)
                count = *osize_p;
        if (count) {
                memmove(output, input, count);
                *isize_p -= count;
                *osize_p -= count;
        }
        return 0;
}

static void null_free_fn(struct stream_filter *filter)
{
        ; /* nothing -- null instances are shared */
}

static struct stream_filter_vtbl null_vtbl = {
        null_filter_fn,
        null_free_fn,
};

static struct stream_filter null_filter_singleton = {
        &null_vtbl,
};

int is_null_stream_filter(struct stream_filter *filter)
{
        return filter == &null_filter_singleton;
}


/*
 * LF-to-CRLF filter
 */

struct lf_to_crlf_filter {
        struct stream_filter filter;
        unsigned has_held:1;
        char held;
};

static int lf_to_crlf_filter_fn(struct stream_filter *filter,
                                const char *input, size_t *isize_p,
                                char *output, size_t *osize_p)
{
        size_t count, o = 0;
        struct lf_to_crlf_filter *lf_to_crlf = (struct lf_to_crlf_filter *)filter;

        /*
         * We may be holding onto the CR to see if it is followed by a
         * LF, in which case we would need to go to the main loop.
         * Otherwise, just emit it to the output stream.
         */
        if (lf_to_crlf->has_held && (lf_to_crlf->held != '\r' || !input)) {
                output[o++] = lf_to_crlf->held;
                lf_to_crlf->has_held = 0;
        }

        /* We are told to drain */
        if (!input) {
                *osize_p -= o;
                return 0;
        }

        count = *isize_p;
        if (count || lf_to_crlf->has_held) {
                size_t i;
                int was_cr = 0;

                if (lf_to_crlf->has_held) {
                        was_cr = 1;
                        lf_to_crlf->has_held = 0;
                }

                for (i = 0; o < *osize_p && i < count; i++) {
                        char ch = input[i];

                        if (ch == '\n') {
                                output[o++] = '\r';
                        } else if (was_cr) {
                                /*
                                 * Previous round saw CR and it is not followed
                                 * by a LF; emit the CR before processing the
                                 * current character.
                                 */
                                output[o++] = '\r';
                        }

                        /*
                         * We may have consumed the last output slot,
                         * in which case we need to break out of this
                         * loop; hold the current character before
                         * returning.
                         */
                        if (*osize_p <= o) {
                                lf_to_crlf->has_held = 1;
                                lf_to_crlf->held = ch;
                                continue; /* break but increment i */
                        }

                        if (ch == '\r') {
                                was_cr = 1;
                                continue;
                        }

                        was_cr = 0;
                        output[o++] = ch;
                }

                *osize_p -= o;
                *isize_p -= i;

                if (!lf_to_crlf->has_held && was_cr) {
                        lf_to_crlf->has_held = 1;
                        lf_to_crlf->held = '\r';
                }
        }
        return 0;
}

static void lf_to_crlf_free_fn(struct stream_filter *filter)
{
        free(filter);
}

static struct stream_filter_vtbl lf_to_crlf_vtbl = {
        lf_to_crlf_filter_fn,
        lf_to_crlf_free_fn,
};

static struct stream_filter *lf_to_crlf_filter(void)
{
        struct lf_to_crlf_filter *lf_to_crlf = xcalloc(1, sizeof(*lf_to_crlf));

        lf_to_crlf->filter.vtbl = &lf_to_crlf_vtbl;
        return (struct stream_filter *)lf_to_crlf;
}

/*
 * Cascade filter
 */
#define FILTER_BUFFER 1024
struct cascade_filter {
        struct stream_filter filter;
        struct stream_filter *one;
        struct stream_filter *two;
        char buf[FILTER_BUFFER];
        int end, ptr;
};

static int cascade_filter_fn(struct stream_filter *filter,
                             const char *input, size_t *isize_p,
                             char *output, size_t *osize_p)
{
        struct cascade_filter *cas = (struct cascade_filter *) filter;
        size_t filled = 0;
        size_t sz = *osize_p;
        size_t to_feed, remaining;

        /*
         * input -- (one) --> buf -- (two) --> output
         */
        while (filled < sz) {
                remaining = sz - filled;

                /* do we already have something to feed two with? */
                if (cas->ptr < cas->end) {
                        to_feed = cas->end - cas->ptr;
                        if (stream_filter(cas->two,
                                          cas->buf + cas->ptr, &to_feed,
                                          output + filled, &remaining))
                                return -1;
                        cas->ptr += (cas->end - cas->ptr) - to_feed;
                        filled = sz - remaining;
                        continue;
                }

                /* feed one from upstream and have it emit into our buffer */
                to_feed = input ? *isize_p : 0;
                if (input && !to_feed)
                        break;
                remaining = sizeof(cas->buf);
                if (stream_filter(cas->one,
                                  input, &to_feed,
                                  cas->buf, &remaining))
                        return -1;
                cas->end = sizeof(cas->buf) - remaining;
                cas->ptr = 0;
                if (input) {
                        size_t fed = *isize_p - to_feed;
                        *isize_p -= fed;
                        input += fed;
                }

                /* do we know that we drained one completely? */
                if (input || cas->end)
                        continue;

                /* tell two to drain; we have nothing more to give it */
                to_feed = 0;
                remaining = sz - filled;
                if (stream_filter(cas->two,
                                  NULL, &to_feed,
                                  output + filled, &remaining))
                        return -1;
                if (remaining == (sz - filled))
                        break; /* completely drained two */
                filled = sz - remaining;
        }
        *osize_p -= filled;
        return 0;
}

static void cascade_free_fn(struct stream_filter *filter)
{
        struct cascade_filter *cas = (struct cascade_filter *)filter;
        free_stream_filter(cas->one);
        free_stream_filter(cas->two);
        free(filter);
}

static struct stream_filter_vtbl cascade_vtbl = {
        cascade_filter_fn,
        cascade_free_fn,
};

static struct stream_filter *cascade_filter(struct stream_filter *one,
                                            struct stream_filter *two)
{
        struct cascade_filter *cascade;

        if (!one || is_null_stream_filter(one))
                return two;
        if (!two || is_null_stream_filter(two))
                return one;

        cascade = xmalloc(sizeof(*cascade));
        cascade->one = one;
        cascade->two = two;
        cascade->end = cascade->ptr = 0;
        cascade->filter.vtbl = &cascade_vtbl;
        return (struct stream_filter *)cascade;
}

/*
 * ident filter
 */
#define IDENT_DRAINING (-1)
#define IDENT_SKIPPING (-2)
struct ident_filter {
        struct stream_filter filter;
        struct strbuf left;
        int state;
        char ident[45]; /* ": x40 $" */
};

static int is_foreign_ident(const char *str)
{
        int i;

        if (prefixcmp(str, "$Id: "))
                return 0;
        for (i = 5; str[i]; i++) {
                if (isspace(str[i]) && str[i+1] != '$')
                        return 1;
        }
        return 0;
}

static void ident_drain(struct ident_filter *ident, char **output_p, size_t *osize_p)
{
        size_t to_drain = ident->left.len;

        if (*osize_p < to_drain)
                to_drain = *osize_p;
        if (to_drain) {
                memcpy(*output_p, ident->left.buf, to_drain);
                strbuf_remove(&ident->left, 0, to_drain);
                *output_p += to_drain;
                *osize_p -= to_drain;
        }
        if (!ident->left.len)
                ident->state = 0;
}

static int ident_filter_fn(struct stream_filter *filter,
                           const char *input, size_t *isize_p,
                           char *output, size_t *osize_p)
{
        struct ident_filter *ident = (struct ident_filter *)filter;
        static const char head[] = "$Id";

        if (!input) {
                /* drain upon eof */
                switch (ident->state) {
                default:
                        strbuf_add(&ident->left, head, ident->state);
                case IDENT_SKIPPING:
                        /* fallthru */
                case IDENT_DRAINING:
                        ident_drain(ident, &output, osize_p);
                }
                return 0;
        }

        while (*isize_p || (ident->state == IDENT_DRAINING)) {
                int ch;

                if (ident->state == IDENT_DRAINING) {
                        ident_drain(ident, &output, osize_p);
                        if (!*osize_p)
                                break;
                        continue;
                }

                ch = *(input++);
                (*isize_p)--;

                if (ident->state == IDENT_SKIPPING) {
                        /*
                         * Skipping until '$' or LF, but keeping them
                         * in case it is a foreign ident.
                         */
                        strbuf_addch(&ident->left, ch);
                        if (ch != '\n' && ch != '$')
                                continue;
                        if (ch == '$' && !is_foreign_ident(ident->left.buf)) {
                                strbuf_setlen(&ident->left, sizeof(head) - 1);
                                strbuf_addstr(&ident->left, ident->ident);
                        }
                        ident->state = IDENT_DRAINING;
                        continue;
                }

                if (ident->state < sizeof(head) &&
                    head[ident->state] == ch) {
                        ident->state++;
                        continue;
                }

                if (ident->state)
                        strbuf_add(&ident->left, head, ident->state);
                if (ident->state == sizeof(head) - 1) {
                        if (ch != ':' && ch != '$') {
                                strbuf_addch(&ident->left, ch);
                                ident->state = 0;
                                continue;
                        }

                        if (ch == ':') {
                                strbuf_addch(&ident->left, ch);
                                ident->state = IDENT_SKIPPING;
                        } else {
                                strbuf_addstr(&ident->left, ident->ident);
                                ident->state = IDENT_DRAINING;
                        }
                        continue;
                }

                strbuf_addch(&ident->left, ch);
                ident->state = IDENT_DRAINING;
        }
        return 0;
}

static void ident_free_fn(struct stream_filter *filter)
{
        struct ident_filter *ident = (struct ident_filter *)filter;
        strbuf_release(&ident->left);
        free(filter);
}

static struct stream_filter_vtbl ident_vtbl = {
        ident_filter_fn,
        ident_free_fn,
};

static struct stream_filter *ident_filter(const unsigned char *sha1)
{
        struct ident_filter *ident = xmalloc(sizeof(*ident));

        sprintf(ident->ident, ": %s $", sha1_to_hex(sha1));
        strbuf_init(&ident->left, 0);
        ident->filter.vtbl = &ident_vtbl;
        ident->state = 0;
        return (struct stream_filter *)ident;
}

/*
 * Return an appropriately constructed filter for the path, or NULL if
 * the contents cannot be filtered without reading the whole thing
 * in-core.
 *
 * Note that you would be crazy to set CRLF, smuge/clean or ident to a
 * large binary blob you would want us not to slurp into the memory!
 */
struct stream_filter *get_stream_filter(const char *path, const unsigned char *sha1)
{
        struct conv_attrs ca;
        enum crlf_action crlf_action;
        struct stream_filter *filter = NULL;

        convert_attrs(&ca, path);

        if (ca.drv && (ca.drv->smudge || ca.drv->clean))
                return filter;

        if (ca.ident)
                filter = ident_filter(sha1);

        crlf_action = input_crlf_action(ca.crlf_action, ca.eol_attr);

        if ((crlf_action == CRLF_BINARY) || (crlf_action == CRLF_INPUT) ||
            (crlf_action == CRLF_GUESS && auto_crlf == AUTO_CRLF_FALSE))
                filter = cascade_filter(filter, &null_filter_singleton);

        else if (output_eol(crlf_action) == EOL_CRLF &&
                 !(crlf_action == CRLF_AUTO || crlf_action == CRLF_GUESS))
                filter = cascade_filter(filter, lf_to_crlf_filter());

        return filter;
}

void free_stream_filter(struct stream_filter *filter)
{
        filter->vtbl->free(filter);
}

int stream_filter(struct stream_filter *filter,
                  const char *input, size_t *isize_p,
                  char *output, size_t *osize_p)
{
        return filter->vtbl->filter(filter, input, isize_p, output, osize_p);
}