Add BLB_write function to allow modification of data in a BLOB

[Noremos]

This PR is part of the JSON implementation. Efficiently writing binary JSON requires modifying a blob. Otherwise, TempSpace is required to use it and convert the data to a blob, significantly increasing overhead.

Additions:

1. New blob functions: BLB_write. It works the same as TempSpace::write
2. New blob functions: BLB_read. It works the same as BLB_seek + BLB_get_data
3. BLB_lseek now works with BLB_put_data (to modify and append data)
4. BLB_lseek now works with BLB_put_segment (to modify and append data)

[hvlad]

Whats wrong or not enough with seek + putSegment ?

[Noremos]

Whats wrong or not enough with seek + putSegment ?

BLB_lseek works only for BLB_get_segment

[hvlad]

Whats wrong or not enough with seek + putSegment ?

BLB_lseek works only for BLB_get_segment

So why not make it work with put too? I suppose it's been done in your PR anyway.

[Noremos]

Whats wrong or not enough with seek + putSegment ?

BLB_lseek works only for BLB_get_segment

So why not make it work with put too? I suppose it's been done in your PR anyway.

Initially, I wanted to implement the same read/write interface as for TempSpace. But I can do this within the BLB_get_segment function.

[hvlad]

Whats wrong or not enough with seek + putSegment ?

BLB_lseek works only for BLB_get_segment

So why not make it work with put too? I suppose it's been done in your PR anyway.

Initially, I wanted to implement the same read/write interface as for TempSpace.

You still speak about blobs here ?

But I can do this within the BLB_get_segment function.

I'm lost your point here, sorry. How it answers on my question ?

[hvlad]

BTW, code in blb.cpp (at least) requires comments. It have none too small useful comments, imo.

[sim1984]

Why is JsonTempParsingTests.cpp needed in this PR?

[Noremos]

Whats wrong or not enough with seek + putSegment ?

BLB_lseek works only for BLB_get_segment

So why not make it work with put too? I suppose it's been done in your PR anyway.

Initially, I wanted to implement the same read/write interface as for TempSpace.

You still speak about blobs here ?

But I can do this within the BLB_get_segment function.

I'm lost your point here, sorry. How it answers on my question ?

I meant that the TempSpace class has convenient read/write functions with the ability to specify a position, so it would be great to have the same function for blobs at some point.

As for BLB_put_data and BLB_put_segment, I initially didn't want to change them, as the code in them is quite complex and modifying it would be quite difficult. But now I see that the integration is quite simple, so I did it.

So now BLB_write works the same as BLB_lseek + BLB_put_data (or BLB_lseek + BLB_put_segment).

[Noremos]

Why is JsonTempParsingTests.cpp needed in this PR?

Sorry, forgot to delete this file after the branch checkout.

[dyemanov]

If you say BLB_write() is convenient, I'd also expect BLB_read() to be added for symmetry.

[aafemt]

Do new methods of blb really need this ancient BLB_ prefix?..

[Noremos]

BTW, code in blb.cpp (at least) requires comments. It have none too small useful comments, imo.

Added description of modification algorithm:
https://github.com/FirebirdSQL/firebird/pull/9066/changes#diff-b38a2d18c3f2097dc3697386a2d4d4cb6c708408ac2cdad4169aca72bdf2479dR2051-R2079

[Noremos]

If you say BLB_write() is convenient, I'd also expect BLB_read() to be added for symmetry.

Added as suggested

[hvlad]

Don't get me wrong - the code itself is not bad, but it is very hard to read, understand and verify.