Render an SVG image as PDF using librsvg2 and cairo.

pdf-to-svg.lua

local ffi = require"ffi"

ffi.cdef[[
// Cairo types
typedef struct _cairo_surface cairo_surface_t;
typedef int cairo_status_t;
typedef struct _cairo cairo_t;

// Poppler types
typedef struct _PopplerPage PopplerPage;
typedef struct _PopplerDocument PopplerDocument;

// Glib types
typedef struct {
    int domain;
    int code;
    char *message;
} GError;
  
// Cairo functions
cairo_surface_t * cairo_svg_surface_create(const char *filename,
                                           double width_in_points,
                                           double height_in_points);
cairo_status_t cairo_surface_status(cairo_surface_t *surface);
cairo_t * cairo_create(cairo_surface_t *);
cairo_status_t cairo_status(cairo_t *cr);
void cairo_show_page(cairo_t *cr);
void cairo_destroy(cairo_t *);
void cairo_surface_destroy(cairo_surface_t *);

// Poppler functions
PopplerDocument * poppler_document_new_from_file(const char *uri,
                                                 const char *password,
                                                 GError **error);
int poppler_document_get_n_pages(PopplerDocument *document);
PopplerPage * poppler_document_get_page(PopplerDocument *document,
                                        int index);
void poppler_page_get_size(PopplerPage *page,
                           double *width,
                           double *height);
void poppler_page_render_for_printing(PopplerPage *page,
                                      cairo_t *cairo);

// Glib functions
char * g_get_current_dir(void);
char * g_build_filename(const char *first_element, ...);
char * g_filename_to_uri(const char *filename,
                         const char *hostname,
                         GError **error);
void g_free(void *);
void g_object_unref(void *);
]]

local POPPLER = ffi.load("poppler-glib") -- libpoppler-glib-dev
local CAIRO = ffi.load("cairo")          -- libcairo2-dev
local GLIB = ffi.load("gobject-2.0")     -- libglib2.0-dev

local CAIRO_STATUS_SUCCESS = 0

local errmessage = error

local function page_to_svg(pdfname, svgname, idx)
    -- Allocate an error object
    local err = ffi.new("GError*[1]", ffi.NULL)

    -- Convert relative path to absolute path
    local currentdir = GLIB.g_get_current_dir()
    local absolutefilename = GLIB.g_build_filename(currentdir, pdfname, ffi.NULL)
    GLIB.g_free(currentdir)

    -- Convert path to URI
    local filename_uri = GLIB.g_filename_to_uri(absolutefilename, ffi.NULL, err)
    GLIB.g_free(absolutefilename)
    if filename_uri == ffi.NULL then
        errmessage(ffi.string(err[0].message))
    end

    -- Open PDF file
    local pdffile = POPPLER.poppler_document_new_from_file(filename_uri, ffi.NULL, err)
    GLIB.g_free(filename_uri)
    if pdffile == ffi.NULL then
        errmessage(ffi.string(err[0].message))
    end

    -- Test page count and get page
    local pagecount = POPPLER.poppler_document_get_n_pages(pdffile)
    if not (idx < pagecount) then
        errmessage("Page out of range (index " .. idx .. " >= " .. pagecount .. " pages)")
    end
    local page = POPPLER.poppler_document_get_page(pdffile, idx)

    -- Get page dimensions
    local width = ffi.new("double[1]")
    local height = ffi.new("double[1]")
    POPPLER.poppler_page_get_size(page, width, height)

    -- Open Cairo surface
    local surface = CAIRO.cairo_svg_surface_create(svgname, width[0], height[0]);
    local status = CAIRO.cairo_surface_status(surface)
    if status ~= CAIRO_STATUS_SUCCESS then
        errmessage("Cairo surface error (code " .. status .. ")")
    end

    -- Open Cairo context
    local cr = CAIRO.cairo_create(surface)
    local status = CAIRO.cairo_status(cr)
    if status ~= CAIRO_STATUS_SUCCESS then
        errmessage("Cairo error (code " .. status .. ")")
    end

    -- Render PDF in Cairo context
    POPPLER.poppler_page_render_for_printing(page, cr)
    CAIRO.cairo_show_page(cr)

    -- Clean up
    if (cr ~= ffi.NULL) then CAIRO.cairo_destroy(cr) end
    if (surface ~= ffi.NULL) then CAIRO.cairo_surface_destroy(surface) end
    if (page ~= ffi.NULL) then GLIB.g_object_unref(page) end
    if (pdffile ~= ffi.NULL) then GLIB.g_object_unref(pdffile) end
    if (err[0] ~= ffi.NULL) then GLIB.g_object_unref(err[0]) end
end

page_to_svg("test.pdf", "test.svg", 0)

svg-to-pdf.c

/*
  Render an SVG image as PDF using librsvg2 and cairo.
  Use with care!
  Also librsvg and cairo leak all over the place.
  clang -Wall -Wextra -Wpedantic \
    -I/usr/include/librsvg-2.0/librsvg/ \
    -I/usr/include/glib-2.0/ \
    -I/usr/lib/x86_64-linux-gnu/glib-2.0/include/ \
    -I/usr/include/gdk-pixbuf-2.0/ \
    -I/usr/include/cairo/ \
    test.c -lcairo -lrsvg-2 -lgobject-2.0
*/

#include <stdio.h>
#include <rsvg.h>
#include <cairo-pdf.h>

static cairo_status_t
rsvg_cairo_write_func(void *closure, unsigned char const *data, unsigned int length) {
    if (fwrite(data, 1, length, (FILE*)closure) == length) {
        return CAIRO_STATUS_SUCCESS;
    }
    return CAIRO_STATUS_WRITE_ERROR;
}

int main()
{
    // Open file
    GError *error = NULL;
    RsvgHandle *rsvg = rsvg_handle_new_from_file("test.svg", &error);
    if (rsvg == NULL) {
        fprintf(stderr, "%s\n", error->message);
        return 1;
    }
    
    // Get size of image
    RsvgDimensionData dimensions;
    rsvg_handle_get_dimensions(rsvg, &dimensions);

    // Open cairo PDF canvas of same size
    FILE *ofile = fopen("test.pdf", "wb");
    cairo_surface_t *surface = cairo_pdf_surface_create_for_stream(
        rsvg_cairo_write_func, ofile, dimensions.width, dimensions.height);
    cairo_status_t status = cairo_surface_status(surface);
    if (status != CAIRO_STATUS_SUCCESS) {
        fprintf(stderr, "Cairo surface error (code %d)\n", status);
        return 1;
    }

    // Render SVG on the canvas
    cairo_t *cr = cairo_create(surface);
    status = cairo_status(cr);
    if (status != CAIRO_STATUS_SUCCESS) {
        fprintf(stderr, "Cairo surface error (code %d)\n", status);
        return 1;
    }
    int success = rsvg_handle_render_cairo(rsvg, cr);
    if (success == FALSE) {
        fprintf(stderr, "Rsvg rendering failed\n");
        return 1;
    }

    // Clean up
    if (cr) { cairo_destroy(cr); }
    if (surface) { cairo_surface_destroy(surface); }
    if (ofile) { fclose(ofile); }
    if (rsvg) { g_object_unref(rsvg); }
    if (error) { g_object_unref(error); }
}

svg-to-pdf.lua

local ffi = require("ffi")

ffi.cdef[[
// Types
typedef struct FILE_tag FILE;
typedef struct RsvgHandle_tag RsvgHandle;
typedef struct cairo_surface_tag cairo_surface_t;
typedef enum cairo_status_tag cairo_status_t;
typedef struct cairo_tag cairo_t;
typedef int (*cairo_write_func_t)(void *, const unsigned char *, unsigned int);

typedef struct {
  int domain;
  int code;
  char *message;
} GError;

typedef struct {
    int width;
    int height;
    double em;
    double ex;
} RsvgDimensionData;

// Conversion functions
RsvgHandle * rsvg_handle_new_from_file(const char *, GError **);
void rsvg_handle_get_dimensions(RsvgHandle *, RsvgDimensionData *);
cairo_surface_t * cairo_pdf_surface_create_for_stream(cairo_write_func_t, FILE *, double, double);
cairo_status_t cairo_surface_status(cairo_surface_t *surface);
cairo_t * cairo_create(cairo_surface_t *);
cairo_status_t cairo_status(cairo_t *cr);
int rsvg_handle_render_cairo(RsvgHandle *, cairo_t *);

// Cleanup functions
void cairo_destroy(cairo_t *);
void cairo_surface_destroy(cairo_surface_t *);
void g_object_unref(void *);
]]

local lcairo = ffi.load("cairo")
local lrsvg = ffi.load("rsvg-2")

local CAIRO_STATUS_SUCCESS = 0
local CAIRO_STATUS_WRITE_ERROR = 11

local ofile = io.open("test.pdf", "wb")
function rsvg_cairo_write_func(_, data, length)
   if (ofile:write(ffi.string(data, length))) then
      return CAIRO_STATUS_SUCCESS
   end
   return CAIRO_STATUS_WRITE_ERROR
end

-- Open input file
local err = ffi.new("GError*[1]", ffi.NULL)
local rsvg = lrsvg.rsvg_handle_new_from_file("test.svg", err)
if rsvg == ffi.NULL then
    error(ffi.string(err[0].message))
end

-- Get size of image
local dimensions = ffi.new("RsvgDimensionData[1]")
lrsvg.rsvg_handle_get_dimensions(rsvg, dimensions)

-- Open cairo PDF canvas of same size
local surface = lcairo.cairo_pdf_surface_create_for_stream(
   rsvg_cairo_write_func, nil, dimensions[0].width, dimensions[0].height)
local status = lcairo.cairo_surface_status(surface)
if status ~= CAIRO_STATUS_SUCCESS then
    error("Cairo surface error (code " .. status .. ")")
end

-- Render SVG on the canvas
local cr = lcairo.cairo_create(surface)
local status = lcairo.cairo_status(cr)
if status ~= CAIRO_STATUS_SUCCESS then
    error("Cairo error (code " .. status .. ")")
end
local success = lrsvg.rsvg_handle_render_cairo(rsvg, cr)
if success == 0 then
    error("Rsvg rendering failed")
end

-- Clean up
if (cr ~= ffi.NULL) then lcairo.cairo_destroy(cr) end
if (surface ~= ffi.NULL) then lcairo.cairo_surface_destroy(surface) end
if (rsvg ~= ffi.NULL) then lrsvg.g_object_unref(rsvg) end
if (err[0] ~= ffi.NULL) then lrsvg.g_object_unref(err[0]) end
ofile:close()