diff --git a/c/Makefile b/c/Makefile
index 9112d84be..b239018c5 100644
--- a/c/Makefile
+++ b/c/Makefile
@@ -99,9 +99,10 @@ mlrp: .always dsls
 
 tests: unit-test reg-test
 
-unit-test: test-mlrutil test-lrec test-join-bucket-keeper
+unit-test: test-mlrutil test-lrec test-string-builder test-join-bucket-keeper
 	./test-mlrutil
 	./test-lrec
+	./test-string-builder
 	./test-join-bucket-keeper
 	@echo
 	@echo DONE
@@ -116,10 +117,11 @@ dev-tests: dev-unit-test reg-test
 
 # Unfortunately --error-exitcode=1 doesn't work well since there are
 # valgrind-detected errors in stdlibs. :(
-dev-unit-test: test-mlrutil test-lrec test-join-bucket-keeper
+dev-unit-test: test-mlrutil test-lrec test-string-builder test-join-bucket-keeper
 	#valgrind --leak-check=full --error-exitcode=1 ./a.out
 	valgrind --leak-check=full ./test-mlrutil
 	valgrind --leak-check=full ./test-lrec
+	valgrind --leak-check=full ./test-string-builder
 	valgrind --leak-check=full ./test-join-bucket-keeper
 	@echo
 	@echo DONE
@@ -138,6 +140,9 @@ test-lrec: .always
 test-mlrutil: .always
 	$(CCDEBUG) -D__TEST_MLRUTIL_MAIN__ lib/mlrutil.c lib/test_mlrutil.c -o test-mlrutil
 
+test-string-builder: .always
+	$(CCDEBUG) -D__TEST_STRING_BUILDER_MAIN__ lib/mlrutil.c lib/mlr_globals.c lib/string_builder.c lib/test_string_builder.c -o test-string-builder
+
 test-join-bucket-keeper: .always
 	$(CCDEBUG) -D__TEST_JOIN_BUCKET_KEEPER_MAIN__ $(TEST_JOIN_BUCKET_KEEPER_SRCS) -o test-join-bucket-keeper
 
diff --git a/c/csv-rfc.txt b/c/csv-rfc.txt
index 7dd4a2c28..dc546678c 100644
--- a/c/csv-rfc.txt
+++ b/c/csv-rfc.txt
@@ -1,3 +1,30 @@
+================================================================
+--> parser option: write a grammar like the below. be careful to
+    preserve the streaming property!
+
+--> state-machine option:
+    * each field either does or does not begin & end w/ "
+    * possibility of "" inside
+    * pretty simple except for CRLF being a double terminator, & fact I cannot
+      use getline anymore
+    * use fgetc & imitate mmap-style seeking
+    * still char irs needs to be char* irs ... and for rfc-csv it's non-parameterizable.
+    * for general string-fs/rs/ps (for other formats) there will need to be some rework.
+
+    * char p,q = lagged-by-one fgetc: while p != EOF.
+    * have a char* get_field(FILE* fp) function.
+    * enter the function looking at start of field.
+
+    * aux-fcn if SOF isn't DQUOTE: just string-build until COMMA, CRLF, or EOF
+    * aux-fcn if SOF is DQUOTE: just string-build until DQUOTE COMMA,
+      DQUOTE CRLF, or DQUOTE EOF. with special case that DQUOTE DQUOTE
+      maps to DQUOTE.
+
+--> regardless: need a string_builder_t with private int curlen, char* buf,
+    public fcn append_char, public fcn append_string,
+    private fcn realloc resizing with minimal copy, public fcn zterm & produce.
+
+================================================================
 Definition of the CSV Format
 
 While there are various specifications and implementations for the
@@ -86,4 +113,3 @@ The ABNF grammar [2] appears as follows:
   CRLF = CR LF ;as per section 6.1 of RFC 2234 [2]
 
   TEXTDATA =  %x20-21 / %x23-2B / %x2D-7E
-
diff --git a/c/lib/string_builder.c b/c/lib/string_builder.c
new file mode 100644
index 000000000..099c653c0
--- /dev/null
+++ b/c/lib/string_builder.c
@@ -0,0 +1,52 @@
+#include <stdlib.h>
+#include <string.h>
+#include "string_builder.h"
+#include "../lib/mlrutil.h"
+#include "../lib/mlr_globals.h"
+
+static void sb_enlarge(string_builder_t* psb);
+
+// typedef struct _string_builder_t {
+//         int used_length;
+//         int alloc_length;
+//         char* buffer;
+// } string_builder_t;
+
+void sb_init(string_builder_t* psb, int alloc_length) {
+	if (alloc_length < 1) {
+		fprintf(stderr, "%s: string_builder alloc_length must be >= 1; got %d.\n",
+			MLR_GLOBALS.argv0, alloc_length);
+		exit(1);
+	}
+	psb->used_length = 0;
+	psb->alloc_length = alloc_length;
+	psb->buffer = mlr_malloc_or_die(alloc_length); // xxx malloc ...
+}
+
+void sb_append_char(string_builder_t* psb, char c) {
+	if (psb->used_length >= psb->alloc_length)
+		sb_enlarge(psb);
+	psb->buffer[psb->used_length++] = c;
+}
+
+void sb_append_string(string_builder_t* psb, char* s) {
+	for (char* p = s; *p; p++)
+		sb_append_char(psb, *p);
+}
+
+char* sb_finish(string_builder_t* psb) {
+	sb_append_char(psb, '\0');
+	char* rv = psb->buffer;
+	psb->used_length  = 0;
+	psb->alloc_length = 0;
+	psb->buffer       = NULL;
+	return rv;
+}
+
+static void sb_enlarge(string_builder_t* psb) {
+	int new_alloc_length = psb->alloc_length * 2;
+	char* new_buffer = mlr_malloc_or_die(new_alloc_length);
+	memcpy(new_buffer, psb->buffer, psb->used_length);
+	psb->alloc_length = new_alloc_length;
+	psb->buffer = new_buffer;
+}
diff --git a/c/lib/string_builder.h b/c/lib/string_builder.h
new file mode 100644
index 000000000..4f40da249
--- /dev/null
+++ b/c/lib/string_builder.h
@@ -0,0 +1,16 @@
+#ifndef STRING_BUILDER_H
+#define STRING_BUILDER_H
+
+typedef struct _string_builder_t {
+	int used_length;
+	int alloc_length;
+	char* buffer;
+} string_builder_t;
+
+void  sb_init(string_builder_t* psb, int alloc_length);
+void  sb_append_char(string_builder_t* psb, char c);
+void  sb_append_string(string_builder_t* psb, char* s);
+// The caller should free() the return value:
+char* sb_finish(string_builder_t* psb);
+
+#endif // STRING_BUILDER_H
diff --git a/c/lib/test_string_builder.c b/c/lib/test_string_builder.c
new file mode 100644
index 000000000..de4d23913
--- /dev/null
+++ b/c/lib/test_string_builder.c
@@ -0,0 +1,95 @@
+#include <stdio.h>
+#include <string.h>
+#include "lib/minunit.h"
+#include "lib/mlrutil.h"
+#include "lib/string_builder.h"
+
+#ifdef __TEST_STRING_BUILDER_MAIN__
+int tests_run         = 0;
+int tests_failed      = 0;
+int assertions_run    = 0;
+int assertions_failed = 0;
+
+// ----------------------------------------------------------------
+static char * test_simple() {
+	string_builder_t sb;
+	string_builder_t* psb = &sb;
+
+	sb_init(psb, 1);
+	mu_assert("error: case 0", streq("", sb_finish(psb)));
+
+	sb_init(psb, 1);
+	sb_append_char(psb, 'a');
+	mu_assert("error: case 1", streq("a", sb_finish(psb)));
+
+	sb_init(psb, 1);
+	sb_append_char(psb, 'a');
+	sb_append_char(psb, 'b');
+	mu_assert("error: case 2", streq("ab", sb_finish(psb)));
+
+	sb_init(psb, 1);
+	sb_append_char(psb, 'a');
+	sb_append_char(psb, 'b');
+	sb_append_char(psb, 'b');
+	sb_append_char(psb, 'c');
+	sb_append_char(psb, 'c');
+	sb_append_char(psb, 'e');
+	mu_assert("error: case 3", streq("abbcce", sb_finish(psb)));
+
+	sb_init(psb, 1);
+	sb_append_string(psb, "");
+	mu_assert("error: case 4", streq("", sb_finish(psb)));
+
+	sb_init(psb, 1);
+	sb_append_string(psb, "hello");
+	mu_assert("error: case 5", streq("hello", sb_finish(psb)));
+
+	sb_init(psb, 1);
+	sb_append_string(psb, "hello");
+	sb_append_char(psb, ',');
+	sb_append_char(psb, ' ');
+	sb_append_string(psb, "world");
+	sb_append_char(psb, '!');
+	mu_assert("error: case 5", streq("hello, world!", sb_finish(psb)));
+
+	sb_init(psb, 2);
+	sb_append_string(psb, "hello");
+	sb_append_char(psb, ',');
+	sb_append_char(psb, ' ');
+	sb_append_string(psb, "world");
+	sb_append_char(psb, '!');
+	mu_assert("error: case 6", streq("hello, world!", sb_finish(psb)));
+
+	sb_init(psb, 32768);
+	sb_append_string(psb, "hello");
+	sb_append_char(psb, ',');
+	sb_append_char(psb, ' ');
+	sb_append_string(psb, "world");
+	sb_append_char(psb, '!');
+	mu_assert("error: case 7", streq("hello, world!", sb_finish(psb)));
+
+	return 0;
+}
+
+// ================================================================
+static char * all_tests() {
+	mu_run_test(test_simple);
+	return 0;
+}
+
+int main(int argc, char **argv) {
+	char *result = all_tests();
+	printf("\n");
+	if (result != 0) {
+		//printf("%s\n", result);
+		printf("Not all unit tests passed\n");
+	}
+	else {
+		printf("TEST_STRING_BUILDER: ALL UNIT TESTS PASSED\n");
+	}
+	printf("Tests      passed: %d of %d\n", tests_run - tests_failed, tests_run);
+	printf("Assertions passed: %d of %d\n", assertions_run - assertions_failed, assertions_run);
+
+	return result != 0;
+}
+#endif // __TEST_STRING_BUILDER_MAIN__