How to insert (raw bytes from file data) using a plain text script - postgresql

Question

Database: Postgres 9.1
I have a table called logos defined like this:
create type image_type as enum ('png');
create table logos (
id UUID primary key,
bytes bytea not null,
type image_type not null,
created timestamp with time zone default current_timestamp not null
);
create index logo_id_idx on logos(id);
I want to be able to insert records into this table in 2 ways.
The first (and most common) way rows will be inserted in the table will be that a user will provide a PNG image file via an html file upload form. The code processing the request on the server will receive a byte array containing the data in the PNG image file and insert a record in the table using something very similar to what is explained here. There are plenty of example of how to insert byte arrays into a postgresql field of type bytea on the internet. This is an easy exercise. An example of the insert code would look like this:
insert into logos (id, bytes, type, created) values (?, ?, ?, now())
And the bytes would be set with something like:
...
byte[] bytes = ... // read PNG file into a byte array.
...
ps.setBytes(2, bytes);
...
The second way rows will be inserted in the table will be from a plain text file script. The reason this is needed is only to populate test data into the table for automated tests, or to initialize the database with a few records for a remote development environment.
Regardless of how the data is entered in the table, the application will obviously need to be able to select the bytea data from the table and convert it back into a PNG image.
Question
How does one properly encode a byte array, to be able to insert the data from within a script, in such a way that only the original bytes contained in the file are stored in the database?
I can write code to read the file and spit out insert statements to populate the script. But I don't know how to encode the byte array for the plain text script such that when running the script from psql the image data will be the same as if the file was inserted using the setBytes jdbc code.
I would like to run the script with something like this:
psql -U username -d dataBase -a -f test_data.sql

Answer 1

The easiest way, IMO, to represent bytea data in an SQL file is to use the hex format:
8.4.1. bytea Hex Format
The "hex" format encodes binary data as 2 hexadecimal digits per byte, most significant nibble first. The entire string is preceded by the sequence \x (to distinguish it from the escape format). In some contexts, the initial backslash may need to be escaped by doubling it, in the same cases in which backslashes have to be doubled in escape format; details appear below. The hexadecimal digits can be either upper or lower case, and whitespace is permitted between digit pairs (but not within a digit pair nor in the starting \x sequence). The hex format is compatible with a wide range of external applications and protocols, and it tends to be faster to convert than the escape format, so its use is preferred.
Example:
SELECT E'\\xDEADBEEF';
Converting an array of bytes to hex should be trivial in any language that a sane person (such a yourself) would use to write the SQL file generator.