From 9cb6d49f4a706dacdb59fdca8f35101fa8cfe3be Mon Sep 17 00:00:00 2001
From: James Kermode <J.R.Kermode@warwick.ac.uk>
Date: Wed, 20 Sep 2023 13:22:40 +0100
Subject: [PATCH] Fix for issue #33

---
 src/fileio.jl |  4 ++--
 test/dict.jl  | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/fileio.jl b/src/fileio.jl
index af8bd5a..694ce7a 100644
--- a/src/fileio.jl
+++ b/src/fileio.jl
@@ -212,7 +212,7 @@ function read_frame_dicts(fp::Ptr{Cvoid}; verbose=false)
             eof = true
             throw(EOFError())
         end
-
+        (nat[] == 0) && error("ExtXYZ frame contains zero atoms. Behaviour is undefined!")
         if verbose
             cprint_dict(info[])
             cprint_dict(arrays[])
@@ -287,7 +287,7 @@ function read_frame(fp::Ptr{Cvoid}; verbose=false)
     return dict
 end
 
-read_frame(file::Union{String,IOStream}, index; kwargs...) = read_frames(file, index; kwargs...)[1]
+read_frame(file::Union{String,IOStream}, index; kwargs...) = only(read_frames(file, index; kwargs...))
 read_frame(file::Union{String,IOStream}; kwargs...) = read_frame(file, 1; kwargs...)
 
 """
diff --git a/test/dict.jl b/test/dict.jl
index bc8d9a5..4653e8e 100644
--- a/test/dict.jl
+++ b/test/dict.jl
@@ -109,6 +109,30 @@ Si        13.00000000      14.00000000      $(frame+1).00000000          0
         @testset "missingfile" begin
             @test_throws ErrorException("file bla.extxyz cannot be opened for reading") read_frame("bla.extxyz")
         end
+
+        @testset "emptyfile" begin
+            s="""
+
+
+            """
+            open(infile, "w") do io
+                print(io, s)
+            end
+            @test_throws ArgumentError("Collection is empty, must contain exactly 1 element") read_frame(infile)
+        end
+
+        @testset "zeroatoms" begin
+            s="""0
+
+
+            """
+            open(infile, "w") do io
+                print(io, s)
+            end
+            ExtXYZ.cfopen(infile) do fp
+                @test_throws ErrorException("ExtXYZ frame contains zero atoms. Behaviour is undefined!") read_frame(fp)
+            end
+        end
     finally
         rm(infile, force=true)
         rm(outfile, force=true)