3 files changed, 34 insertions, 3 deletions
diff --git a/src/core/transport/chttp2/stream_encoder.c b/src/core/transport/chttp2/stream_encoder.c
index 0f04169741..1ea697f71e 100644
--- a/src/core/transport/chttp2/stream_encoder.c
+++ b/src/core/transport/chttp2/stream_encoder.c
@@ -66,6 +66,8 @@ typedef struct {
   size_t header_idx;
   /* was the last frame emitted a header? (if yes, we'll need a CONTINUATION */
   gpr_uint8 last_was_header;
+  /* have we seen a regular (non-colon-prefixed) header yet? */
+  gpr_uint8 seen_regular_header;
   /* output stream id */
   gpr_uint32 stream_id;
   gpr_slice_buffer *output;
@@ -361,6 +363,15 @@ static grpc_mdelem *hpack_enc(grpc_chttp2_hpack_compressor *c,
   gpr_uint32 indices_key;
   int should_add_elem;
 
+  GPR_ASSERT (GPR_SLICE_LENGTH(elem->key->slice) > 0);
+  if (GPR_SLICE_START_PTR(elem->key->slice)[0] != ':') { /* regular header */
+    st->seen_regular_header = 1;
+  } else if (st->seen_regular_header != 0) { /* reserved header */
+    gpr_log(GPR_ERROR,
+            "Reserved header (colon-prefixed) happening after regular ones.");
+    abort();
+  }
+
   inc_filter(HASH_FRAGMENT_1(elem_hash), &c->filter_elems_sum, c->filter_elems);
 
   /* is this elem currently in the decoders table? */
@@ -566,6 +577,7 @@ void grpc_chttp2_encode(grpc_stream_op *ops, size_t ops_count, int eof,
 
   st.cur_frame_type = NONE;
   st.last_was_header = 0;
+  st.seen_regular_header = 0;
   st.stream_id = stream_id;
   st.output = output;
 
diff --git a/src/core/transport/metadata.c b/src/core/transport/metadata.c
index f92e87e9dd..3fd21a2f5d 100644
--- a/src/core/transport/metadata.c
+++ b/src/core/transport/metadata.c
@@ -681,16 +681,34 @@ void grpc_mdctx_locked_mdelem_unref(grpc_mdctx *ctx,
 
 void grpc_mdctx_unlock(grpc_mdctx *ctx) { unlock(ctx); }
 
-int grpc_mdstr_is_legal_header(grpc_mdstr *s) {
-  /* TODO(ctiller): consider caching this, or computing it on construction */
+static int conforms_to(grpc_mdstr *s, const gpr_uint8 *legal_bits) {
   const gpr_uint8 *p = GPR_SLICE_START_PTR(s->slice);
   const gpr_uint8 *e = GPR_SLICE_END_PTR(s->slice);
   for (; p != e; p++) {
-    if (*p < 32 || *p > 126) return 0;
+    int idx = *p;
+    int byte = idx / 8;
+    int bit = idx % 8;
+    if ((legal_bits[byte] & (1 << bit)) == 0) return 0;
   }
   return 1;
 }
 
+int grpc_mdstr_is_legal_header(grpc_mdstr *s) {
+  static const gpr_uint8 legal_header_bits[256 / 8] = {
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0xff, 0x03, 0x00, 0x00, 0x00,
+      0x80, 0xfe, 0xff, 0xff, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+  return conforms_to(s, legal_header_bits);
+}
+
+int grpc_mdstr_is_legal_nonbin_header(grpc_mdstr *s) {
+  static const gpr_uint8 legal_header_bits[256 / 8] = {
+      0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+      0xff, 0xff, 0xff, 0xff, 0x7f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+  return conforms_to(s, legal_header_bits);
+}
+
 int grpc_mdstr_is_bin_suffixed(grpc_mdstr *s) {
   /* TODO(ctiller): consider caching this */
   return grpc_is_binary_header((const char *)GPR_SLICE_START_PTR(s->slice),
diff --git a/src/core/transport/metadata.h b/src/core/transport/metadata.h
index a7af49ba55..eb17747be7 100644
--- a/src/core/transport/metadata.h
+++ b/src/core/transport/metadata.h
@@ -154,6 +154,7 @@ void grpc_mdelem_unref(grpc_mdelem *md);
 const char *grpc_mdstr_as_c_string(grpc_mdstr *s);
 
 int grpc_mdstr_is_legal_header(grpc_mdstr *s);
+int grpc_mdstr_is_legal_nonbin_header(grpc_mdstr *s);
 int grpc_mdstr_is_bin_suffixed(grpc_mdstr *s);
 
 /* Batch mode metadata functions.