cgotpl

C99 golang-style template engine

Be careful with untrusted input!

Usage

cgotpl comes with a simple CLI.

cgotpl [TEMPLATE] [DATA]

Here TEMPLATE refers to a golang-style template string and DATA to a serialized JSON string. For instance:

cgotpl '{{ range . -}} {{.}} {{- end }}' '["h", "e", "ll", "o"]'

Will print hello on stdout.

API

There's a single central function defined in template.h:

// tpl is a pointer to a template string from which up to n bytes are read.
// dot is the inital dot value. out will be filled with the result of templating
// and needs to be freed by the caller. Returns 0 on success.
int template_eval(const char* tpl, size_t n, json_value* dot, char** out);

An initalized json_value can be obtained from:

// Consumes an abitrary amount of bytes from st to parse a single JSON value
// into val. Returns 0 on success.
int json_parse(stream* st, json_value* val);

A json_value needs to be freed with:

void json_value_free(json_value* val);

A stream can be created with:

// Opens stream backed by data up to len bytes.
void stream_open_memory(stream* stream, const void* data, size_t len);
// Opens stream on the file referenced by filename. Returns 0 on success.
int stream_open_file(stream* stream, const char* filename);

A stream needs be closed with:

// Closes stream. Returns 0 on success.
int stream_close(stream* stream);

See cli/main.c for a complete example.

Building

cmake version 3.16 or greater is required. Initialize cmake with:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release

The following will produce the cgotpl CLI in build/cli/cgotpl:

cmake --build build --target cli

The library can be build with:

cmake --build build --target cgotpl

For development a check (requires a go compiler) and fuzz (requires CC=clang) target exist.

Features

Currently, basic control-flow and data access is implemented.

Feature	State
Trim whitespace {{- and -}}	✅
{{/* comments */}}	❌
Default Textual Representation {{pipeline}}	✅
Literals	🚧 (Some escape sequences are missing)
{{if pipeline}} T1 {{end}}	✅
{{if pipeline}} T1 {{else}} T0 {{end}}	✅
{{if p}} T1 {{else if p}} T0 {{end}}	✅
{{range pipeline}} T1 {{end}}	✅
{{range pipeline}} T1 {{else}} T0 {{end}}	✅
{{break}}	✅
{{continue}}	✅
{{define}}	❌
{{template "name" pipeline}}	❌
{{block "name" pipeline}} T1 {{end}}	❌
{{with pipeline}} T1 {{end}}	❌
Field access .a.b.c	✅
Variables	❌
Functions (e.g. printf, not, and, ...)	❌

The c and go standard library may disagree on certain formatting (printf) corner-cases. cgotpl parses non-executed templates sloppy. Syntactical issues in non-executed branches may not lead to an error.

Why?

I wanted to make something in C.