Introducing octet_length(): The Savior for Accurate Blob Size in SQLite

• Hidden size information: SQLite doesn't explicitly store the size of blobs within the database file. It calculates the length on the fly when needed.
• length() function: While the length() function in SQLite usually returns the number of bytes for blobs, it can be unreliable if the blob contains null characters (\0). These characters mark the end of strings in some programming languages, and length() might stop counting at the first null byte encountered, giving you an incorrect size.

Solutions:

Here are two approaches to find the accurate length of a binary blob:

Using length() with Caution:

This method works well if you're certain your blobs don't contain null characters.

SELECT id, length(blob_data) AS blob_size
FROM your_table;

This query selects the id and the length() of the blob_data column, aliasing it as blob_size.

Using octet_length() (SQLite 3.43 and later):

If you're using SQLite version 3.43 or later, you can utilize the new octet_length() function. This function specifically returns the number of bytes in a blob, regardless of null characters.

SELECT id, octet_length(blob_data) AS blob_size
FROM your_table;

This query is similar to the previous one, but it uses octet_length() instead of length().

Related Issues and Solutions:

• Encrypted blobs: If your blobs are encrypted, neither length() nor octet_length() will give you the original size. You'll need to decrypt the blob before finding its length.
• Older SQLite versions: If you're using an older version of SQLite, consider upgrading to take advantage of octet_length(). Alternatively, you can write custom functions in C or other languages to access the blob size using the C/C++ API, but this requires more advanced knowledge.

Remember:

• Be aware of potential limitations and edge cases when working with blobs.
• Choose the method that best suits your SQLite version and blob content.