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From d7b56e186521ce2e48e27edda121d780a3d62d27 Mon Sep 17 00:00:00 2001
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From: Jan Synacek <jsynacek@redhat.com>
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Date: Thu, 23 Nov 2017 08:53:50 +0100
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Subject: [PATCH] fileio: add new helper call read_line() as bounded getline()
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 replacement
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read_line() is much like getline(), and returns a line read from a
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FILE*, of arbitrary sizes. In contrast to gets() it will grow the buffer
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dynamically, and in contrast to getline() it will place a user-specified
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boundary on the line.
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(cherry-picked from commit 4f9a66a32dda1d9a28f9bb3fa31c2148524bc46a)
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Resolves: #1503106
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---
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 src/shared/fileio.c    | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++
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 src/shared/fileio.h    |  2 ++
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 src/test/test-fileio.c | 44 +++++++++++++++++++++++++++++
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 3 files changed, 123 insertions(+)
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diff --git a/src/shared/fileio.c b/src/shared/fileio.c
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index ff6b1a7ed..107737573 100644
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--- a/src/shared/fileio.c
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+++ b/src/shared/fileio.c
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@@ -815,3 +815,80 @@ int get_status_field(const char *filename, const char *pattern, char **field) {
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         return 0;
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 }
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+
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+int read_line(FILE *f, size_t limit, char **ret) {
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+        _cleanup_free_ char *buffer = NULL;
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+        size_t n = 0, allocated = 0, count = 0;
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+        int r;
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+
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+        assert(f);
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+
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+        /* Something like a bounded version of getline().
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+         *
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+         * Considers EOF, \n and \0 end of line delimiters, and does not include these delimiters in the string
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+         * returned.
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+         *
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+         * Returns the number of bytes read from the files (i.e. including delimiters — this hence usually differs from
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+         * the number of characters in the returned string). When EOF is hit, 0 is returned.
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+         *
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+         * The input parameter limit is the maximum numbers of characters in the returned string, i.e. excluding
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+         * delimiters. If the limit is hit we fail and return -ENOBUFS.
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+         *
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+         * If a line shall be skipped ret may be initialized as NULL. */
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+
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+        if (ret) {
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+                if (!GREEDY_REALLOC(buffer, allocated, 1))
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+                        return -ENOMEM;
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+        }
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+
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+        flockfile(f);
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+
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+        for (;;) {
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+                int c;
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+
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+                if (n >= limit) {
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+                        funlockfile(f);
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+                        return -ENOBUFS;
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+                }
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+
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+                errno = 0;
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+                c = fgetc_unlocked(f);
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+                if (c == EOF) {
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+                        /* if we read an error, and have no data to return, then propagate the error */
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+                        if (ferror_unlocked(f) && n == 0) {
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+                                r = errno > 0 ? -errno : -EIO;
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+                                funlockfile(f);
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+                                return r;
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+                        }
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+
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+                        break;
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+                }
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+
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+                count++;
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+
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+                if (IN_SET(c, '\n', 0)) /* Reached a delimiter */
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+                        break;
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+
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+                if (ret) {
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+                        if (!GREEDY_REALLOC(buffer, allocated, n + 2)) {
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+                                funlockfile(f);
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+                                return -ENOMEM;
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+                        }
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+
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+                        buffer[n] = (char) c;
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+                }
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+
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+                n++;
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+        }
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+
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+        funlockfile(f);
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+
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+        if (ret) {
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+                buffer[n] = 0;
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+
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+                *ret = buffer;
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+                buffer = NULL;
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+        }
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+
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+        return (int) count;
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+}
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diff --git a/src/shared/fileio.h b/src/shared/fileio.h
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index 5ae51c1e2..f33464dce 100644
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--- a/src/shared/fileio.h
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+++ b/src/shared/fileio.h
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@@ -43,3 +43,5 @@ int write_env_file(const char *fname, char **l);
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 int executable_is_script(const char *path, char **interpreter);
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 int get_status_field(const char *filename, const char *pattern, char **field);
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+
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+int read_line(FILE *f, size_t limit, char **ret);
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diff --git a/src/test/test-fileio.c b/src/test/test-fileio.c
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index 63e4a19b7..fc5969322 100644
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--- a/src/test/test-fileio.c
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+++ b/src/test/test-fileio.c
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@@ -392,6 +392,49 @@ static void test_load_env_file_pairs(void) {
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         unlink(fn);
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 }
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+static void test_read_line(void) {
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+        _cleanup_fclose_ FILE *f = NULL;
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+        _cleanup_free_ char *line = NULL;
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+
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+        char buffer[] =
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+                "Some test data\n"
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+                "With newlines, and a NUL byte\0"
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+                "\n"
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+                "an empty line\n"
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+                "an ignored line\n"
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+                "and a very long line that is supposed to be truncated, because it is so long\n";
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+
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+        f = fmemopen(buffer, sizeof(buffer), "re");
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+        assert_se(f);
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+
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+        assert_se(read_line(f, (size_t) -1, &line) == 15 && streq(line, "Some test data"));
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+        line = mfree(line);
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+
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+        assert_se(read_line(f, 1024, &line) == 30 && streq(line, "With newlines, and a NUL byte"));
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+        line = mfree(line);
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+
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+        assert_se(read_line(f, 1024, &line) == 1 && streq(line, ""));
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+        line = mfree(line);
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+
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+        assert_se(read_line(f, 1024, &line) == 14 && streq(line, "an empty line"));
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+        line = mfree(line);
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+
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+        assert_se(read_line(f, (size_t) -1, NULL) == 16);
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+
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+        assert_se(read_line(f, 16, &line) == -ENOBUFS);
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+        line = mfree(line);
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+
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+        /* read_line() stopped when it hit the limit, that means when we continue reading we'll read at the first
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+         * character after the previous limit. Let's make use of tha to continue our test. */
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+        assert_se(read_line(f, 1024, &line) == 61 && streq(line, "line that is supposed to be truncated, because it is so long"));
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+        line = mfree(line);
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+
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+        assert_se(read_line(f, 1024, &line) == 1 && streq(line, ""));
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+        line = mfree(line);
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+
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+        assert_se(read_line(f, 1024, &line) == 0 && streq(line, ""));
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+}
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+
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 int main(int argc, char *argv[]) {
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         log_parse_environment();
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         log_open();
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@@ -405,6 +448,7 @@ int main(int argc, char *argv[]) {
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         test_write_string_file();
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         test_write_string_file_no_create();
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         test_load_env_file_pairs();
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+        test_read_line();
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         return 0;
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 }