io-util: split out "struct iovec" related calls into their own .c/.h files

This is preparation for #28891, which adds a bunch more helpers around
"struct iovec", at which point this really deserves its own .c/.h file.

The idea is that we sooner or later can consider "struct iovec" as an
entirely generic mechanism to reference some binary blob, and is the
go-to type for this purpose whenever we need one.

1 files changed, 53 insertions, 0 deletions

diff --git a/src/basic/iovec-util.h b/src/basic/iovec-util.h
new file mode 100644
index 0000000000..7ee72671c4
--- /dev/null
+++ b/src/basic/iovec-util.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <stdbool.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+
+#include "macro.h"
+
+static inline size_t IOVEC_TOTAL_SIZE(const struct iovec *i, size_t n) {
+        size_t r = 0;
+
+        for (size_t j = 0; j < n; j++)
+                r += i[j].iov_len;
+
+        return r;
+}
+
+static inline bool IOVEC_INCREMENT(struct iovec *i, size_t n, size_t k) {
+        /* Returns true if there is nothing else to send (bytes written cover all of the iovec),
+         * false if there's still work to do. */
+
+        for (size_t j = 0; j < n; j++) {
+                size_t sub;
+
+                if (i[j].iov_len == 0)
+                        continue;
+                if (k == 0)
+                        return false;
+
+                sub = MIN(i[j].iov_len, k);
+                i[j].iov_len -= sub;
+                i[j].iov_base = (uint8_t*) i[j].iov_base + sub;
+                k -= sub;
+        }
+
+        assert(k == 0); /* Anything else would mean that we wrote more bytes than available,
+                         * or the kernel reported writing more bytes than sent. */
+        return true;
+}
+
+#define IOVEC_NULL (struct iovec) {}
+#define IOVEC_MAKE(base, len) (struct iovec) { .iov_base = (base), .iov_len = (len) }
+#define IOVEC_MAKE_STRING(string)               \
+        ({                                      \
+                char *_s = (char*) (string);    \
+                IOVEC_MAKE(_s, strlen(_s));     \
+        })
+
+char* set_iovec_string_field(struct iovec *iovec, size_t *n_iovec, const char *field, const char *value);
+char* set_iovec_string_field_free(struct iovec *iovec, size_t *n_iovec, const char *field, char *value);
+
+void iovec_array_free(struct iovec *iov, size_t n);