Prepare for streaming interface

src/test.cpp

@@ -415,15 +415,30 @@ private:
 // Table-based ll(1) parser that doesn't handle escaping and treats numbers as
 // [0-9.]+. Could be adapted to have a streaming interface. Uses O(1) memory.
 struct Parser2 {
-  Parser2(char *buf, int len, const Callbacks *callbacks, void *data)
+  Parser2(const Callbacks *callbacks, void *data)
-      : buf(buf), bufEnd(buf + len), callbacks(callbacks), data(data) {}
+      : callbacks(callbacks), data(data) {}
 
-  // Returns false to reject
+  void prime(char *buf, int len) {
-  [[nodiscard]] bool parse() {
+    this->buf = buf;
-    if (push({N_VALUE}) != S_OK) {
+    this->bufEnd = buf + len;
-      return false;
   }
-    return keepGoing(this) == S_OK;
+
+  enum Status {
+    // Accept input
+    S_OK,
+    // Consumed available input. Prime more and parse again
+    S_AGAIN,
+    // Invalid json
+    S_REJECT,
+    // json is too deeply nested
+    S_OVERFLOW,
+  };
+
+  [[nodiscard]] Status parse() {
+    if (Status s = push({N_VALUE})) {
+      return s;
+    }
+    return keepGoing(this);
   }
 
   Parser2(Parser2 const &) = delete;
@@ -433,13 +448,6 @@ struct Parser2 {
 
   static constexpr int kMaxStackSize = 1 << 10;
 
-  enum Status {
-    S_OK,
-    S_AGAIN,
-    S_REJECT,
-    S_OVERFLOW,
-  };
-
 private:
   // Helpers
   void maybeSkipWs() {
@@ -632,8 +640,8 @@ private:
       /*N_OBJECT_MAYBE_CONTINUE*/ objectContinue,
   };
 
-  char *buf;
+  char *buf = nullptr;
-  char *bufEnd;
+  char *bufEnd = nullptr;
   int len() const { return bufEnd - buf; }
   const Callbacks *const callbacks;
   void *const data;
@@ -724,13 +732,23 @@ TEST_CASE("parser2") {
   Callbacks c = printCallbacks();
   {
     auto copy = json;
-    Parser2 parser(copy.data(), copy.length(), &c, nullptr);
+    Parser2 parser(&c, nullptr);
-    CHECK(parser.parse());
+    parser.prime(copy.data(), copy.length());
+    CHECK(parser.parse() == Parser2::S_OK);
   }
   {
     std::string copy = "{\"x\": [], \"y\": {}}";
-    Parser2 parser(copy.data(), copy.length(), &c, nullptr);
+    Parser2 parser(&c, nullptr);
-    CHECK(parser.parse());
+    parser.prime(copy.data(), copy.length());
+    CHECK(parser.parse() == Parser2::S_OK);
+  }
+  {
+    std::string copy = "true";
+    Parser2 parser(&c, nullptr);
+    parser.prime(copy.data(), 2);
+    CHECK(parser.parse() == Parser2::S_AGAIN);
+    parser.prime(copy.data() + 2, 2);
+    CHECK(parser.parse() == Parser2::S_OK);
   }
 }
 
@@ -753,7 +771,8 @@ TEST_CASE("bench2") {
   bench.unit("byte");
   bench.run("parser2", [&]() {
     auto copy = json;
-    Parser2 parser(copy.data(), copy.length(), &c, nullptr);
+    Parser2 parser(&c, nullptr);
+    parser.prime(copy.data(), copy.length());
     bench.doNotOptimizeAway(parser.parse());
   });
 }