Merge pull request #14555 from poettering/table-multine

format-table: proper multi-line support

src/basic/string-util.c

@@ -1074,3 +1074,121 @@ char* string_erase(char *x) {
         explicit_bzero_safe(x, strlen(x));
         return x;
 }
+
+int string_truncate_lines(const char *s, size_t n_lines, char **ret) {
+        const char *p = s, *e = s;
+        bool truncation_applied = false;
+        char *copy;
+        size_t n = 0;
+
+        assert(s);
+
+        /* Truncate after the specified number of lines. Returns > 0 if a truncation was applied or == 0 if
+         * there were fewer lines in the string anyway. Trailing newlines on input are ignored, and not
+         * generated either. */
+
+        for (;;) {
+                size_t k;
+
+                k = strcspn(p, "\n");
+
+                if (p[k] == 0) {
+                        if (k == 0) /* final empty line */
+                                break;
+
+                        if (n >= n_lines) /* above threshold */
+                                break;
+
+                        e = p + k; /* last line to include */
+                        break;
+                }
+
+                assert(p[k] == '\n');
+
+                if (n >= n_lines)
+                        break;
+
+                if (k > 0)
+                        e = p + k;
+
+                p += k + 1;
+                n++;
+        }
+
+        /* e points after the last character we want to keep */
+        if (isempty(e))
+                copy = strdup(s);
+        else {
+                if (!in_charset(e, "\n")) /* We only consider things truncated if we remove something that
+                                           * isn't a new-line or a series of them */
+                        truncation_applied = true;
+
+                copy = strndup(s, e - s);
+        }
+        if (!copy)
+                return -ENOMEM;
+
+        *ret = copy;
+        return truncation_applied;
+}
+
+int string_extract_line(const char *s, size_t i, char **ret) {
+        const char *p = s;
+        size_t c = 0;
+
+        /* Extract the i'nth line from the specified string. Returns > 0 if there are more lines after that,
+         * and == 0 if we are looking at the last line or already beyond the last line. As special
+         * optimization, if the first line is requested and the string only consists of one line we return
+         * NULL, indicating the input string should be used as is, and avoid a memory allocation for a very
+         * common case. */
+
+        for (;;) {
+                const char *q;
+
+                q = strchr(p, '\n');
+                if (i == c) {
+                        /* The line we are looking for! */
+
+                        if (q) {
+                                char *m;
+
+                                m = strndup(p, q - p);
+                                if (!m)
+                                        return -ENOMEM;
+
+                                *ret = m;
+                                return !isempty(q + 1); /* more coming? */
+                        } else {
+                                if (p == s)
+                                        *ret = NULL; /* Just use the input string */
+                                else {
+                                        char *m;
+
+                                        m = strdup(p);
+                                        if (!m)
+                                                return -ENOMEM;
+
+                                        *ret = m;
+                                }
+
+                                return 0; /* The end */
+                        }
+                }
+
+                if (!q) {
+                        char *m;
+
+                        /* No more lines, return empty line */
+
+                        m = strdup("");
+                        if (!m)
+                                return -ENOMEM;
+
+                        *ret = m;
+                        return 0; /* The end */
+                }
+
+                p = q + 1;
+                c++;
+        }
+}

src/basic/string-util.h

@@ -280,3 +280,6 @@ static inline char* str_realloc(char **p) {
 }
 
 char* string_erase(char *x);
+
+int string_truncate_lines(const char *s, size_t n_lines, char **ret);
+int string_extract_line(const char *s, size_t i, char **ret);