For the purpose of applying the patch and committing the results,
implement extracting the patch data, commit message and authorship from
an e-mail message using git-mailinfo.

git-mailinfo is run as a separate process, but ideally in the future,
we should be be able to access its functionality directly without
spawning a new process.

Helped-by: Junio C Hamano <gits...@pobox.com>
Helped-by: Jeff King <p...@peff.net>
Helped-by: Johannes Schindelin <johannes.schinde...@gmx.de>
Signed-off-by: Paul Tan <pyoka...@gmail.com>
---
 builtin/am.c | 317 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 317 insertions(+)

diff --git a/builtin/am.c b/builtin/am.c
index c12566a..63f0fa4 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -9,6 +9,23 @@
 #include "parse-options.h"
 #include "dir.h"
 #include "run-command.h"
+#include "quote.h"
+
+/**
+ * Returns 1 if the file is empty or does not exist, 0 otherwise.
+ */
+static int is_empty_file(const char *filename)
+{
+       struct stat st;
+
+       if (stat(filename, &st) < 0) {
+               if (errno == ENOENT)
+                       return 1;
+               die_errno(_("could not stat %s"), filename);
+       }
+
+       return !st.st_size;
+}
 
 /**
  * Like strbuf_getline(), but treats both '\n' and "\r\n" as line terminators.
@@ -38,6 +55,13 @@ struct am_state {
        int cur;
        int last;
 
+       /* commit metadata and message */
+       char *author_name;
+       char *author_email;
+       char *author_date;
+       char *msg;
+       size_t msg_len;
+
        /* number of digits in patch filename */
        int prec;
 };
@@ -62,6 +86,10 @@ static void am_state_init(struct am_state *state, const char 
*dir)
 static void am_state_release(struct am_state *state)
 {
        free(state->dir);
+       free(state->author_name);
+       free(state->author_email);
+       free(state->author_date);
+       free(state->msg);
 }
 
 /**
@@ -112,6 +140,161 @@ static int read_state_file(struct strbuf *sb, const 
struct am_state *state,
 }
 
 /**
+ * Reads a KEY=VALUE shell variable assignment from `fp`, returning the VALUE
+ * as a newly-allocated string. VALUE must be a quoted string, and the KEY must
+ * match `key`. Returns NULL on failure.
+ *
+ * This is used by read_author_script() to read the GIT_AUTHOR_* variables from
+ * the author-script.
+ */
+static char *read_shell_var(FILE *fp, const char *key)
+{
+       struct strbuf sb = STRBUF_INIT;
+       const char *str;
+
+       if (strbuf_getline(&sb, fp, '\n'))
+               goto fail;
+
+       if (!skip_prefix(sb.buf, key, &str))
+               goto fail;
+
+       if (!skip_prefix(str, "=", &str))
+               goto fail;
+
+       strbuf_remove(&sb, 0, str - sb.buf);
+
+       str = sq_dequote(sb.buf);
+       if (!str)
+               goto fail;
+
+       return strbuf_detach(&sb, NULL);
+
+fail:
+       strbuf_release(&sb);
+       return NULL;
+}
+
+/**
+ * Reads and parses the state directory's "author-script" file, and sets
+ * state->author_name, state->author_email and state->author_date accordingly.
+ * Returns 0 on success, -1 if the file could not be parsed.
+ *
+ * The author script is of the format:
+ *
+ *     GIT_AUTHOR_NAME='$author_name'
+ *     GIT_AUTHOR_EMAIL='$author_email'
+ *     GIT_AUTHOR_DATE='$author_date'
+ *
+ * where $author_name, $author_email and $author_date are quoted. We are strict
+ * with our parsing, as the file was meant to be eval'd in the old git-am.sh
+ * script, and thus if the file differs from what this function expects, it is
+ * better to bail out than to do something that the user does not expect.
+ */
+static int read_author_script(struct am_state *state)
+{
+       const char *filename = am_path(state, "author-script");
+       FILE *fp;
+
+       assert(!state->author_name);
+       assert(!state->author_email);
+       assert(!state->author_date);
+
+       fp = fopen(filename, "r");
+       if (!fp) {
+               if (errno == ENOENT)
+                       return 0;
+               die_errno(_("could not open '%s' for reading"), filename);
+       }
+
+       state->author_name = read_shell_var(fp, "GIT_AUTHOR_NAME");
+       if (!state->author_name) {
+               fclose(fp);
+               return -1;
+       }
+
+       state->author_email = read_shell_var(fp, "GIT_AUTHOR_EMAIL");
+       if (!state->author_email) {
+               fclose(fp);
+               return -1;
+       }
+
+       state->author_date = read_shell_var(fp, "GIT_AUTHOR_DATE");
+       if (!state->author_date) {
+               fclose(fp);
+               return -1;
+       }
+
+       if (fgetc(fp) != EOF) {
+               fclose(fp);
+               return -1;
+       }
+
+       fclose(fp);
+       return 0;
+}
+
+/**
+ * Saves state->author_name, state->author_email and state->author_date in the
+ * state directory's "author-script" file.
+ */
+static void write_author_script(const struct am_state *state)
+{
+       struct strbuf sb = STRBUF_INIT;
+
+       strbuf_addstr(&sb, "GIT_AUTHOR_NAME=");
+       sq_quote_buf(&sb, state->author_name);
+       strbuf_addch(&sb, '\n');
+
+       strbuf_addstr(&sb, "GIT_AUTHOR_EMAIL=");
+       sq_quote_buf(&sb, state->author_email);
+       strbuf_addch(&sb, '\n');
+
+       strbuf_addstr(&sb, "GIT_AUTHOR_DATE=");
+       sq_quote_buf(&sb, state->author_date);
+       strbuf_addch(&sb, '\n');
+
+       write_file(am_path(state, "author-script"), 1, "%s", sb.buf);
+
+       strbuf_release(&sb);
+}
+
+/**
+ * Reads the commit message from the state directory's "final-commit" file,
+ * setting state->msg to its contents and state->msg_len to the length of its
+ * contents in bytes.
+ *
+ * Returns 0 on success, -1 if the file does not exist.
+ */
+static int read_commit_msg(struct am_state *state)
+{
+       struct strbuf sb = STRBUF_INIT;
+
+       assert(!state->msg);
+
+       if (read_state_file(&sb, state, "final-commit", 0) < 0) {
+               strbuf_release(&sb);
+               return -1;
+       }
+
+       state->msg = strbuf_detach(&sb, &state->msg_len);
+       return 0;
+}
+
+/**
+ * Saves state->msg in the state directory's "final-commit" file.
+ */
+static void write_commit_msg(const struct am_state *state)
+{
+       int fd;
+       const char *filename = am_path(state, "final-commit");
+
+       fd = xopen(filename, O_WRONLY | O_CREAT, 0666);
+       if (write_in_full(fd, state->msg, state->msg_len) < 0)
+               die_errno(_("could not write to %s"), filename);
+       close(fd);
+}
+
+/**
  * Loads state from disk.
  */
 static void am_load(struct am_state *state)
@@ -126,6 +309,11 @@ static void am_load(struct am_state *state)
                die("BUG: state file 'last' does not exist");
        state->last = strtol(sb.buf, NULL, 10);
 
+       if (read_author_script(state) < 0)
+               die(_("could not parse author script"));
+
+       read_commit_msg(state);
+
        strbuf_release(&sb);
 }
 
@@ -318,19 +506,148 @@ static void am_setup(struct am_state *state, enum 
patch_format patch_format,
  */
 static void am_next(struct am_state *state)
 {
+       free(state->author_name);
+       state->author_name = NULL;
+
+       free(state->author_email);
+       state->author_email = NULL;
+
+       free(state->author_date);
+       state->author_date = NULL;
+
+       free(state->msg);
+       state->msg = NULL;
+       state->msg_len = 0;
+
+       unlink(am_path(state, "author-script"));
+       unlink(am_path(state, "final-commit"));
+
        state->cur++;
        write_file(am_path(state, "next"), 1, "%d", state->cur);
 }
 
 /**
+ * Returns the filename of the current patch email.
+ */
+static const char *msgnum(const struct am_state *state)
+{
+       static struct strbuf sb = STRBUF_INIT;
+
+       strbuf_reset(&sb);
+       strbuf_addf(&sb, "%0*d", state->prec, state->cur);
+
+       return sb.buf;
+}
+
+/**
+ * Parses `mail` using git-mailinfo, extracting its patch and authorship info.
+ * state->msg will be set to the patch message. state->author_name,
+ * state->author_email and state->author_date will be set to the patch author's
+ * name, email and date respectively. The patch body will be written to the
+ * state directory's "patch" file.
+ *
+ * Returns 1 if the patch should be skipped, 0 otherwise.
+ */
+static int parse_mail(struct am_state *state, const char *mail)
+{
+       FILE *fp;
+       struct child_process cp = CHILD_PROCESS_INIT;
+       struct strbuf sb = STRBUF_INIT;
+       struct strbuf msg = STRBUF_INIT;
+       struct strbuf author_name = STRBUF_INIT;
+       struct strbuf author_date = STRBUF_INIT;
+       struct strbuf author_email = STRBUF_INIT;
+       int ret = 0;
+
+       cp.git_cmd = 1;
+       cp.in = xopen(mail, O_RDONLY, 0);
+       cp.out = xopen(am_path(state, "info"), O_WRONLY | O_CREAT, 0777);
+
+       argv_array_push(&cp.args, "mailinfo");
+       argv_array_push(&cp.args, am_path(state, "msg"));
+       argv_array_push(&cp.args, am_path(state, "patch"));
+
+       if (run_command(&cp) < 0)
+               die("could not parse patch");
+
+       close(cp.in);
+       close(cp.out);
+
+       /* Extract message and author information */
+       fp = xfopen(am_path(state, "info"), "r");
+       while (!strbuf_getline(&sb, fp, '\n')) {
+               const char *x;
+
+               if (skip_prefix(sb.buf, "Subject: ", &x)) {
+                       if (msg.len)
+                               strbuf_addch(&msg, '\n');
+                       strbuf_addstr(&msg, x);
+               } else if (skip_prefix(sb.buf, "Author: ", &x))
+                       strbuf_addstr(&author_name, x);
+               else if (skip_prefix(sb.buf, "Email: ", &x))
+                       strbuf_addstr(&author_email, x);
+               else if (skip_prefix(sb.buf, "Date: ", &x))
+                       strbuf_addstr(&author_date, x);
+       }
+       fclose(fp);
+
+       /* Skip pine's internal folder data */
+       if (!strcmp(author_name.buf, "Mail System Internal Data")) {
+               ret = 1;
+               goto finish;
+       }
+
+       if (is_empty_file(am_path(state, "patch"))) {
+               printf_ln(_("Patch is empty. Was it split wrong?"));
+               exit(128);
+       }
+
+       strbuf_addstr(&msg, "\n\n");
+       if (strbuf_read_file(&msg, am_path(state, "msg"), 0) < 0)
+               die_errno(_("could not read '%s'"), am_path(state, "msg"));
+       stripspace(&msg, 0);
+
+       assert(!state->author_name);
+       state->author_name = strbuf_detach(&author_name, NULL);
+
+       assert(!state->author_email);
+       state->author_email = strbuf_detach(&author_email, NULL);
+
+       assert(!state->author_date);
+       state->author_date = strbuf_detach(&author_date, NULL);
+
+       assert(!state->msg);
+       state->msg = strbuf_detach(&msg, &state->msg_len);
+
+finish:
+       strbuf_release(&msg);
+       strbuf_release(&author_date);
+       strbuf_release(&author_email);
+       strbuf_release(&author_name);
+       strbuf_release(&sb);
+       return ret;
+}
+
+/**
  * Applies all queued mail.
  */
 static void am_run(struct am_state *state)
 {
        while (state->cur <= state->last) {
+               const char *mail = am_path(state, msgnum(state));
+
+               if (!file_exists(mail))
+                       goto next;
+
+               if (parse_mail(state, mail))
+                       goto next; /* mail should be skipped */
+
+               write_author_script(state);
+               write_commit_msg(state);
 
                /* NEEDSWORK: Patch application not implemented yet */
 
+next:
                am_next(state);
        }
 
-- 
2.5.0.280.gd88bd6e

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