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fix(cairo_render): fix UB #46

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fix(cairo_render): fix UB #46

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19 changes: 15 additions & 4 deletions src/cairo.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -45,11 +45,13 @@ end

const julia_cairo_engine = Ref{gvdevice_engine_t}()
const julia_cairo_features = Ref{gvdevice_features_t}(gvdevice_features_t(Int32(0),0.,0.,0.,0.,96.,96.))
const julia_cairo_name = Vector{UInt8}("julia:cairo")
const julia_cairo_libname = Vector{UInt8}("julia:cairo")
const julia_cairo_name = vcat(Vector{UInt8}("julia:cairo"), UInt8(0))
const julia_cairo_libname = vcat(Vector{UInt8}("julia:cairo"), UInt8(0))
const julia_cairo_device = Ref{NTuple{2, gvplugin_installed_t}}()
const julia_cairo_api = Ref{NTuple{2, gvplugin_api_t}}()

format_placeholder = Vector{UInt8}()

function init_cairo_structs!()
julia_cairo_engine[] = gvdevice_engine_t(@cfunction(cairo_initialize,Cvoid,(Ptr{Cvoid},)),@cfunction(cairo_format,Cvoid,(Ptr{Cvoid},)),@cfunction(cairo_finalize,Cvoid,(Ptr{Cvoid},)))
julia_cairo_device[] = (
Expand Down Expand Up @@ -80,12 +82,21 @@ function render(c::CairoContext,g::GraphViz.Graph; context = default_context[],
end

function cairo_render(g::GraphViz.Graph; context = default_context[], format="julia:cairo")
global last_surface
global last_surface, format_placeholder
GraphViz.add_julia_cairo!(context)
if !g.didlayout
error("Must call layout before calling render!")
end
ccall((:gvRenderContext,libgvc),Cint,(Ptr{Cvoid},Ptr{Cvoid},Ptr{UInt8},Ptr{Cvoid}),context.handle,g.handle,format,C_NULL)

empty!(format_placeholder)
append!(format_placeholder, format)
push!(format_placeholder, UInt8(0))
format_cstring = pointer(format_placeholder)

ret = ccall((:gvRenderContext,libgvc),Cint,(Ptr{Cvoid},Ptr{Cvoid},Ptr{UInt8},Ptr{Cvoid}),context.handle,g.handle,format_cstring,C_NULL)
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@Keno Keno May 19, 2025

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This is all not gc-safe. Just declare this as Cstring rather than Ptr{UInt8} and let julia worry about the string conversion.

if ret != 0
error("gvRenderContext failed with return code: $ret")
end
surface = last_surface
last_surface = nothing
return surface
Expand Down