Add buffer/push-at for easier manipulation of buffers

buffer/blit is difficult to use, and while buffer/push is the easiet
buffer manipulation function to use it only appends to the buffer.
buffer/push-at lets users manipulate buffers at any index - useful
for buffers used as an in-memory databases, for example.

CHANGELOG.md

@@ -2,6 +2,7 @@
 All notable changes to this project will be documented in this file.
 
 ## ??? - Unreleased
+- Add `buffer/push-at`
 - Add `ffi/pointer-buffer` to convert pointers to buffers the cannot be reallocated. This
   allows easier manipulation of FFI memory, memory mapped files, and buffer memory shared between threads.
 - Calling `ev/cancel` on a fiber waiting on `ev/gather` will correctly

src/core/buffer.c

@@ -307,17 +307,8 @@ JANET_CORE_FN(cfun_buffer_chars,
     return argv[0];
 }
 
-JANET_CORE_FN(cfun_buffer_push,
-              "(buffer/push buffer & xs)",
-              "Push both individual bytes and byte sequences to a buffer. For each x in xs, "
-              "push the byte if x is an integer, otherwise push the bytesequence to the buffer. "
-              "Thus, this function behaves like both `buffer/push-string` and `buffer/push-byte`. "
-              "Returns the modified buffer. "
-              "Will throw an error if the buffer overflows.") {
-    int32_t i;
-    janet_arity(argc, 1, -1);
-    JanetBuffer *buffer = janet_getbuffer(argv, 0);
-    for (i = 1; i < argc; i++) {
+static void buffer_push_impl(JanetBuffer *buffer, Janet *argv, int32_t argc_offset, int32_t argc) {
+    for (int32_t i = argc_offset; i < argc; i++) {
         if (janet_checktype(argv[i], JANET_NUMBER)) {
             janet_buffer_push_u8(buffer, (uint8_t)(janet_getinteger(argv, i) & 0xFF));
         } else {
@@ -329,6 +320,36 @@ JANET_CORE_FN(cfun_buffer_push,
             janet_buffer_push_bytes(buffer, view.bytes, view.len);
         }
     }
+}
+
+JANET_CORE_FN(cfun_buffer_push_at,
+              "(buffer/push-at buffer index & xs)",
+              "Same as buffer/push, but inserts new data at index `index`.") {
+    janet_arity(argc, 2, -1);
+    JanetBuffer *buffer = janet_getbuffer(argv, 0);
+    int32_t index = janet_getinteger(argv, 1);
+    int32_t old_count = buffer->count;
+    if (index < 0 || index > old_count) {
+        janet_panicf("index out of range [0, %d)", old_count);
+    }
+    buffer->count = index;
+    buffer_push_impl(buffer, argv, 2, argc);
+    if (buffer->count < old_count) {
+        buffer->count = old_count;
+    }
+    return argv[0];
+}
+
+JANET_CORE_FN(cfun_buffer_push,
+              "(buffer/push buffer & xs)",
+              "Push both individual bytes and byte sequences to a buffer. For each x in xs, "
+              "push the byte if x is an integer, otherwise push the bytesequence to the buffer. "
+              "Thus, this function behaves like both `buffer/push-string` and `buffer/push-byte`. "
+              "Returns the modified buffer. "
+              "Will throw an error if the buffer overflows.") {
+    janet_arity(argc, 1, -1);
+    JanetBuffer *buffer = janet_getbuffer(argv, 0);
+    buffer_push_impl(buffer, argv, 1, argc);
     return argv[0];
 }
 
@@ -492,6 +513,7 @@ void janet_lib_buffer(JanetTable *env) {
         JANET_CORE_REG("buffer/push-word", cfun_buffer_word),
         JANET_CORE_REG("buffer/push-string", cfun_buffer_chars),
         JANET_CORE_REG("buffer/push", cfun_buffer_push),
+        JANET_CORE_REG("buffer/push-at", cfun_buffer_push_at),
         JANET_CORE_REG("buffer/popn", cfun_buffer_popn),
         JANET_CORE_REG("buffer/clear", cfun_buffer_clear),
         JANET_CORE_REG("buffer/slice", cfun_buffer_slice),

src/core/ffi.c

@@ -1374,7 +1374,7 @@ JANET_CORE_FN(cfun_ffi_call,
 
 JANET_CORE_FN(cfun_ffi_buffer_write,
               "(ffi/write ffi-type data &opt buffer)",
-              "Append a native tyep to a buffer such as it would appear in memory. This can be used "
+              "Append a native type to a buffer such as it would appear in memory. This can be used "
               "to pass pointers to structs in the ffi, or send C/C++/native structs over the network "
               "or to files. Returns a modifed buffer or a new buffer if one is not supplied.") {
     janet_sandbox_assert(JANET_SANDBOX_FFI);

test/suite0015.janet

@@ -19,7 +19,6 @@
                symbolslots)
         "symbolslots survive disasm/asm")
 
-# need to fix upvalues
 (comment
   (setdyn *debug* true)
   (setdyn :pretty-format "%.40M")
@@ -41,4 +40,9 @@
                  [3 7 4 'z]])
         "arg & inner symbolslots")
 
+# buffer/push-at
+(assert (deep= @"abc456" (buffer/push-at @"abc123" 3 "456")) "buffer/push-at 1")
+(assert (deep= @"abc456789" (buffer/push-at @"abc123" 3 "456789")) "buffer/push-at 2")
+(assert (deep= @"abc423" (buffer/push-at @"abc123" 3 "4")) "buffer/push-at 3")
+
 (end-suite)