[api] Eliminate intermediate buffers in protobuf dump helpers (#13742)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/api/api_pb2_dump.cpp

@@ -23,15 +23,8 @@ static inline void append_field_prefix(DumpBuffer &out, const char *field_name,
   out.append(indent, ' ').append(field_name).append(": ");
 }
 
-static inline void append_with_newline(DumpBuffer &out, const char *str) {
-  out.append(str);
-  out.append("\n");
-}
-
 static inline void append_uint(DumpBuffer &out, uint32_t value) {
-  char buf[16];
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRIu32, value));
-  snprintf(buf, sizeof(buf), "%" PRIu32, value);
-  out.append(buf);
 }
 
 // RAII helper for message dump formatting
@@ -49,31 +42,23 @@ class MessageDumpHelper {
 
 // Helper functions to reduce code duplication in dump methods
 static void dump_field(DumpBuffer &out, const char *field_name, int32_t value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%" PRId32, value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRId32 "\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, uint32_t value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%" PRIu32, value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRIu32 "\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, float value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%g", value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%g\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, uint64_t value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%" PRIu64, value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRIu64 "\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, bool value, int indent = 2) {
@@ -112,7 +97,7 @@ static void dump_bytes_field(DumpBuffer &out, const char *field_name, const uint
   char hex_buf[format_hex_pretty_size(160)];
   append_field_prefix(out, field_name, indent);
   format_hex_pretty_to(hex_buf, data, len);
-  append_with_newline(out, hex_buf);
+  out.append(hex_buf).append("\n");
 }
 
 template<> const char *proto_enum_to_string<enums::EntityCategory>(enums::EntityCategory value) {

esphome/components/api/proto.h

@@ -402,6 +402,20 @@ class DumpBuffer {
   const char *c_str() const { return buf_; }
   size_t size() const { return pos_; }
 
+  /// Get writable buffer pointer for use with buf_append_printf
+  char *data() { return buf_; }
+  /// Get current position for use with buf_append_printf
+  size_t pos() const { return pos_; }
+  /// Update position after buf_append_printf call
+  void set_pos(size_t pos) {
+    if (pos >= CAPACITY) {
+      pos_ = CAPACITY - 1;
+    } else {
+      pos_ = pos;
+    }
+    buf_[pos_] = '\0';
+  }
+
  private:
   void append_impl_(const char *str, size_t len) {
     size_t space = CAPACITY - 1 - pos_;

script/api_protobuf/api_protobuf.py

@@ -2599,15 +2599,8 @@ static inline void append_field_prefix(DumpBuffer &out, const char *field_name,
   out.append(indent, ' ').append(field_name).append(": ");
 }
 
-static inline void append_with_newline(DumpBuffer &out, const char *str) {
-  out.append(str);
-  out.append("\\n");
-}
-
 static inline void append_uint(DumpBuffer &out, uint32_t value) {
-  char buf[16];
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRIu32, value));
-  snprintf(buf, sizeof(buf), "%" PRIu32, value);
-  out.append(buf);
 }
 
 // RAII helper for message dump formatting
@@ -2625,31 +2618,23 @@ class MessageDumpHelper {
 
 // Helper functions to reduce code duplication in dump methods
 static void dump_field(DumpBuffer &out, const char *field_name, int32_t value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%" PRId32, value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRId32 "\\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, uint32_t value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%" PRIu32, value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRIu32 "\\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, float value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%g", value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%g\\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, uint64_t value, int indent = 2) {
-  char buffer[64];
   append_field_prefix(out, field_name, indent);
-  snprintf(buffer, 64, "%" PRIu64, value);
+  out.set_pos(buf_append_printf(out.data(), DumpBuffer::CAPACITY, out.pos(), "%" PRIu64 "\\n", value));
-  append_with_newline(out, buffer);
 }
 
 static void dump_field(DumpBuffer &out, const char *field_name, bool value, int indent = 2) {
@@ -2689,7 +2674,7 @@ static void dump_bytes_field(DumpBuffer &out, const char *field_name, const uint
   char hex_buf[format_hex_pretty_size(160)];
   append_field_prefix(out, field_name, indent);
   format_hex_pretty_to(hex_buf, data, len);
-  append_with_newline(out, hex_buf);
+  out.append(hex_buf).append("\\n");
 }
 
 """