no-pad: add toplevel -p option to disable frame padding

This enables sending runt frames. This is useful for testing on NPI
ports and frame injection where IFH is prepended, so the wire length is
above 60 bytes, while the frame data may be below.

Author: jeso-mchp

CMakeLists.txt

@@ -96,6 +96,7 @@ add_executable(ef-tests
     test/ef-tests.cxx
     test/test-ef-parse-bytes.cxx
     test/ifh-ignore.cxx
+    test/test-padding.cxx
 )
 
 target_link_libraries(ef-tests libef)

src/ef-args.c

@@ -90,6 +90,8 @@ void print_help() {
     po("Options:\n");
     po("  -v                    Print version.\n");
     po("  -h                    Top level help message.\n");
+    po("  -p                    No pad. Skip padding frames to 60 bytes,\n");
+    po("     allowing runt frames to be sent or matched as-is.\n");
     po("  -t <timeout-in-ms>    When listening on an interface (rx),\n");
     po("     When listening on an interface (rx), the tool will always\n");
     po("     listen during the entire timeout period. This is needed,\n");
@@ -320,13 +322,18 @@ int argc_cmds(int argc, const char *argv[]) {
     return res;
 }
 
+int NO_PAD = 0;
 int TIME_OUT_MS = 100;
 
 int main_(int argc, const char *argv[]) {
     int opt;
 
-    while ((opt = getopt(argc, (char * const*)argv, "vht:c:")) != -1) {
+    while ((opt = getopt(argc, (char * const*)argv, "pvht:c:")) != -1) {
         switch (opt) {
+            case 'p':
+                NO_PAD = 1;
+                break;
+
             case 'v':
                 print_version();
                 return 0;

src/ef.c

@@ -477,7 +477,7 @@ buf_t *frame_to_buf(frame_t *f) {
         frame_size += f->stack[i]->size;
     }
 
-    if (frame_size < 60)
+    if (frame_size < 60 && !NO_PAD)
         frame_size = 60;
 
     buf = balloc(frame_size);
@@ -503,7 +503,7 @@ buf_t *frame_mask_to_buf(frame_t *f) {
     }
 
     frame_size_no_padding = frame_size;
-    if (frame_size < 60)
+    if (frame_size < 60 && !NO_PAD)
         frame_size = 60;
 
     buf = balloc(frame_size);

src/ef.h

@@ -16,6 +16,7 @@ extern "C" {
 #define DIV_ROUND(a, b) (1 + ((a - 1) / b))
 #define BIT_TO_BYTE(x) (DIV_ROUND(x, 8))
 
+extern int NO_PAD;
 extern int TIME_OUT_MS;
 
 ///////////////////////////////////////////////////////////////////////////////

test/test-padding.cxx

@@ -0,0 +1,98 @@
+#include "ef.h"
+#include "ef-test.h"
+#include "catch_single_include.hxx"
+
+#include <cstring>
+
+// RAII guard to set NO_PAD for the duration of a scope
+struct NoPadGuard {
+    NoPadGuard()  { NO_PAD = 1; }
+    ~NoPadGuard() { NO_PAD = 0; }
+};
+
+// Build a frame and its expected buf/mask from a frame spec
+static void build_frame(std::vector<const char *> spec,
+                        buf_t **out_buf, buf_t **out_mask,
+                        frame_t **out_frame)
+{
+    frame_t *f = parse_frame_wrap(spec);
+    REQUIRE(f != NULL);
+    *out_buf = frame_to_buf(f);
+    REQUIRE(*out_buf != NULL);
+    *out_mask = f->has_mask ? frame_mask_to_buf(f) : NULL;
+    *out_frame = f;
+}
+
+TEST_CASE("no-pad: eth-only frame is 14 bytes", "[nopad]") {
+    NoPadGuard g;
+    buf_t *buf, *mask;
+    frame_t *f;
+    build_frame({"eth", "dmac", "::1", "smac", "::2"}, &buf, &mask, &f);
+
+    // eth header = 14 bytes, no padding to 60
+    CHECK(buf->size == 14);
+
+    bfree(buf);
+    frame_free(f);
+}
+
+TEST_CASE("no-pad: default pads to 60 bytes", "[nopad]") {
+    CHECK(NO_PAD == 0);
+    buf_t *buf, *mask;
+    frame_t *f;
+    build_frame({"eth", "dmac", "::1", "smac", "::2"}, &buf, &mask, &f);
+
+    CHECK(buf->size == 60);
+
+    bfree(buf);
+    frame_free(f);
+}
+
+TEST_CASE("no-pad: mask buf also skips padding", "[nopad]") {
+    NoPadGuard g;
+
+    // Use 'ign' on smac to force mask generation
+    frame_t *f = parse_frame_wrap({"eth", "dmac", "::1", "smac", "ign"});
+    REQUIRE(f != NULL);
+    buf_t *buf = frame_to_buf(f);
+    buf_t *mask = frame_mask_to_buf(f);
+    REQUIRE(buf != NULL);
+    REQUIRE(mask != NULL);
+
+    CHECK(buf->size == 14);
+    CHECK(mask->size == 14);
+
+    bfree(buf);
+    bfree(mask);
+    frame_free(f);
+}
+
+TEST_CASE("no-pad: frame with payload stays exact size", "[nopad]") {
+    NoPadGuard g;
+    buf_t *buf, *mask;
+    frame_t *f;
+
+    // eth(14) + data pattern cnt 4 = 18 bytes, well under 60
+    build_frame({"eth", "dmac", "::1", "smac", "::2",
+                 "data", "pattern", "cnt", "4"}, &buf, &mask, &f);
+
+    CHECK(buf->size == 18);
+
+    bfree(buf);
+    frame_free(f);
+}
+
+TEST_CASE("no-pad: large frame unaffected", "[nopad]") {
+    NoPadGuard g;
+    buf_t *buf, *mask;
+    frame_t *f;
+
+    // eth(14) + data pattern cnt 100 = 114 bytes, already > 60
+    build_frame({"eth", "dmac", "::1", "smac", "::2",
+                 "data", "pattern", "cnt", "100"}, &buf, &mask, &f);
+
+    CHECK(buf->size == 114);
+
+    bfree(buf);
+    frame_free(f);
+}